PEP-8 long lines and dunders (#245)

This patch massively reformats the whole codebase mainly wrapping
long lines and eliminating dundered private attributes.

31 files changed, 1786 insertions, 1153 deletions

diff --git a/pysnmp/proto/acmod/rfc3415.py b/pysnmp/proto/acmod/rfc3415.py
index fb4c4adf..13d9de12 100644
--- a/pysnmp/proto/acmod/rfc3415.py
+++ b/pysnmp/proto/acmod/rfc3415.py
@@ -17,65 +17,63 @@ class Vacm(object):
 
     _powOfTwoSeq = (128, 64, 32, 16, 8, 4, 2, 1)
 
-    def isAccessAllowed(self,
-                        snmpEngine,
-                        securityModel,
-                        securityName,
-                        securityLevel,
-                        viewType,
-                        contextName,
-                        variableName):
+    def isAccessAllowed(self, snmpEngine, securityModel, securityName,
+                        securityLevel, viewType, contextName, variableName):
+
         mibInstrumController = snmpEngine.msgAndPduDsp.mibInstrumController
+        mibBuilder = mibInstrumController.mibBuilder
 
         debug.logger & debug.FLAG_ACL and debug.logger(
-            'isAccessAllowed: securityModel %s, securityName %s, securityLevel %s, viewType %s, contextName %s for variableName %s' % (
-                securityModel, securityName, securityLevel, viewType, contextName, variableName))
+            'isAccessAllowed: securityModel %s, securityName %s, '
+            'securityLevel %s, viewType %s, contextName %s for '
+            'variableName %s' % (securityModel, securityName, securityLevel,
+                                 viewType, contextName, variableName))
 
         # 3.2.1
-        vacmContextEntry, = mibInstrumController.mibBuilder.importSymbols(
+        vacmContextEntry, = mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
 
         tblIdx = vacmContextEntry.getInstIdFromIndices(contextName)
+
         try:
             vacmContextEntry.getNode(
-                vacmContextEntry.name + (1,) + tblIdx
-            ).syntax
+                vacmContextEntry.name + (1,) + tblIdx).syntax
 
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noSuchContext)
 
         # 3.2.2
-        vacmSecurityToGroupEntry, = mibInstrumController.mibBuilder.importSymbols(
+        vacmSecurityToGroupEntry, = mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmSecurityToGroupEntry')
+
         tblIdx = vacmSecurityToGroupEntry.getInstIdFromIndices(
-            securityModel, securityName
-        )
+            securityModel, securityName)
 
         try:
             vacmGroupName = vacmSecurityToGroupEntry.getNode(
-                vacmSecurityToGroupEntry.name + (3,) + tblIdx
-            ).syntax
+                vacmSecurityToGroupEntry.name + (3,) + tblIdx).syntax
 
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noGroupName)
 
         # 3.2.3
-        vacmAccessEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry'
-        )
+        vacmAccessEntry, = mibBuilder.importSymbols(
+            'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry')
 
         # XXX partial context name match
         tblIdx = vacmAccessEntry.getInstIdFromIndices(
-            vacmGroupName, contextName, securityModel, securityLevel
-        )
+            vacmGroupName, contextName, securityModel, securityLevel)
 
         # 3.2.4
         if viewType == 'read':
             entryIdx = vacmAccessEntry.name + (5,) + tblIdx
+
         elif viewType == 'write':
             entryIdx = vacmAccessEntry.name + (6,) + tblIdx
+
         elif viewType == 'notify':
             entryIdx = vacmAccessEntry.name + (7,) + tblIdx
+
         else:
             raise error.ProtocolError('Unknown view type %s' % viewType)
 
@@ -93,19 +91,20 @@ class Vacm(object):
         # 3.2.5a
         vacmViewTreeFamilyEntry, = mibInstrumController.mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmViewTreeFamilyEntry')
+
         tblIdx = vacmViewTreeFamilyEntry.getInstIdFromIndices(viewName)
 
         # Walk over entries
         initialTreeName = treeName = vacmViewTreeFamilyEntry.name + (2,) + tblIdx
+
         maskName = vacmViewTreeFamilyEntry.name + (3,) + tblIdx
 
         while True:
             vacmViewTreeFamilySubtree = vacmViewTreeFamilyEntry.getNextNode(
-                treeName
-            )
+                treeName)
+
             vacmViewTreeFamilyMask = vacmViewTreeFamilyEntry.getNextNode(
-                maskName
-            )
+                maskName)
 
             treeName = vacmViewTreeFamilySubtree.name
             maskName = vacmViewTreeFamilyMask.name
@@ -125,10 +124,12 @@ class Vacm(object):
 
                 m = len(mask) - 1
                 idx = l - 1
+
                 while idx:
                     if (idx > m or mask[idx] and
                             vacmViewTreeFamilySubtree.syntax[idx] != variableName[idx]):
                         break
+
                     idx -= 1
 
                 if idx:
diff --git a/pysnmp/proto/acmod/void.py b/pysnmp/proto/acmod/void.py
index 2f8c4e97..e3ee848f 100644
--- a/pysnmp/proto/acmod/void.py
+++ b/pysnmp/proto/acmod/void.py
@@ -15,17 +15,11 @@ class Vacm(object):
     """Void Access Control Model"""
     ACCESS_MODEL_ID = 0
 
-    def isAccessAllowed(self,
-                        snmpEngine,
-                        securityModel,
-                        securityName,
-                        securityLevel,
-                        viewType,
-                        contextName,
-                        variableName):
+    def isAccessAllowed(self, snmpEngine, securityModel, securityName,
+                        securityLevel, viewType, contextName, variableName):
         debug.logger & debug.FLAG_ACL and debug.logger(
-            'isAccessAllowed: viewType %s for variableName %s - OK' % (viewType, variableName)
-        )
+            'isAccessAllowed: viewType %s for variableName '
+            '%s - OK' % (viewType, variableName))
 
         # rfc3415 3.2.5c
         return error.StatusInformation(errorIndication=errind.accessAllowed)
diff --git a/pysnmp/proto/api/v1.py b/pysnmp/proto/api/v1.py
index 827a6a0d..f13920e7 100644
--- a/pysnmp/proto/api/v1.py
+++ b/pysnmp/proto/api/v1.py
@@ -39,10 +39,18 @@ class VarBindAPI(object):
     @staticmethod
     def setOIDVal(varBind, oidVal):
         oid, val = oidVal[0], oidVal[1]
+
         varBind.setComponentByPosition(0, oid)
+
         if val is None:
             val = null
-        varBind.setComponentByPosition(1).getComponentByPosition(1).setComponentByType(val.getTagSet(), val, verifyConstraints=False, matchTags=False, matchConstraints=False, innerFlag=True)
+
+        (varBind.setComponentByPosition(1)
+         .getComponentByPosition(1)
+         .setComponentByType(val.getTagSet(), val,
+                             verifyConstraints=False, matchTags=False,
+                             matchConstraints=False, innerFlag=True))
+
         return varBind
 
     @staticmethod
@@ -61,14 +69,17 @@ class PDUAPI(object):
 
     def setDefaults(self, pdu):
         pdu.setComponentByPosition(
-            0, getNextRequestID(), verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, getNextRequestID(), verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            1, self._errorStatus, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, self._errorStatus, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            2, self._errorIndex, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._errorIndex, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(3)
 
     @staticmethod
@@ -90,12 +101,14 @@ class PDUAPI(object):
     @staticmethod
     def getErrorIndex(pdu, muteErrors=False):
         errorIndex = pdu.getComponentByPosition(2)
+
         if errorIndex > len(pdu[3]):
             if muteErrors:
                 return errorIndex.clone(len(pdu[3]))
+
             raise error.ProtocolError(
-                'Error index out of range: %s > %s' % (errorIndex, len(pdu[3]))
-            )
+                'Error index out of range: %s > %s' % (errorIndex, len(pdu[3])))
+
         return errorIndex
 
     @staticmethod
@@ -119,20 +132,23 @@ class PDUAPI(object):
 
     @staticmethod
     def getVarBinds(pdu):
-        return [apiVarBind.getOIDVal(varBind) for varBind in pdu.getComponentByPosition(3)]
+        return [apiVarBind.getOIDVal(varBind)
+                for varBind in pdu.getComponentByPosition(3)]
 
     @staticmethod
     def setVarBinds(pdu, varBinds):
         varBindList = pdu.setComponentByPosition(3).getComponentByPosition(3)
+
         varBindList.clear()
+
         for idx, varBind in enumerate(varBinds):
             if isinstance(varBind, VarBind):
                 varBindList.setComponentByPosition(idx, varBind)
+
             else:
                 varBindList.setComponentByPosition(idx)
                 apiVarBind.setOIDVal(
-                    varBindList.getComponentByPosition(idx), varBind
-                )
+                    varBindList.getComponentByPosition(idx), varBind)
 
     def getResponse(self, reqPDU):
         rspPDU = GetResponsePDU()
@@ -143,8 +159,10 @@ class PDUAPI(object):
     def getVarBindTable(self, reqPDU, rspPDU):
         if apiPDU.getErrorStatus(rspPDU) == 2:
             varBindRow = [(vb[0], null) for vb in apiPDU.getVarBinds(reqPDU)]
+
         else:
             varBindRow = apiPDU.getVarBinds(rspPDU)
+
         return [varBindRow]
 
     def getNextVarBinds(self, varBinds, errorIndex=None):
@@ -173,14 +191,32 @@ class TrapPDUAPI(object):
             try:
                 import socket
                 agentAddress = IpAddress(socket.gethostbyname(socket.gethostname()))
+
             except Exception:
                 agentAddress = IpAddress('0.0.0.0')
+
             self._networkAddress = NetworkAddress().setComponentByPosition(0, agentAddress)
-        pdu.setComponentByPosition(0, self._entOid, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(1, self._networkAddress, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(2, self._genericTrap, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(3, self._zeroInt, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(4, self._zeroTime, verifyConstraints=False, matchTags=False, matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            0, self._entOid, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            1, self._networkAddress, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            2, self._genericTrap, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            3, self._zeroInt, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            4, self._zeroTime, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(5)
 
     @staticmethod
@@ -197,7 +233,9 @@ class TrapPDUAPI(object):
 
     @staticmethod
     def setAgentAddr(pdu, value):
-        pdu.setComponentByPosition(1).getComponentByPosition(1).setComponentByPosition(0, value)
+        (pdu.setComponentByPosition(1)
+         .getComponentByPosition(1)
+         .setComponentByPosition(0, value))
 
     @staticmethod
     def getGenericTrap(pdu):
@@ -233,24 +271,28 @@ class TrapPDUAPI(object):
 
     @staticmethod
     def getVarBinds(pdu):
-        varBinds = []
-        for varBind in pdu.getComponentByPosition(5):
-            varBinds.append(apiVarBind.getOIDVal(varBind))
-        return varBinds
+        return [apiVarBind.getOIDVal(varBind)
+                for varBind in pdu.getComponentByPosition(5)]
 
     @staticmethod
     def setVarBinds(pdu, varBinds):
         varBindList = pdu.setComponentByPosition(5).getComponentByPosition(5)
+
         varBindList.clear()
+
         idx = 0
+
         for varBind in varBinds:
             if isinstance(varBind, VarBind):
                 varBindList.setComponentByPosition(idx, varBind)
+
             else:
                 varBindList.setComponentByPosition(idx)
+
                 apiVarBind.setOIDVal(
                     varBindList.getComponentByPosition(idx), varBind
                 )
+
             idx += 1
 
 
@@ -262,8 +304,14 @@ class MessageAPI(object):
     _community = univ.OctetString('public')
 
     def setDefaults(self, msg):
-        msg.setComponentByPosition(0, self._version, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        msg.setComponentByPosition(1, self._community, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        msg.setComponentByPosition(
+            0, self._version, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        msg.setComponentByPosition(
+            1, self._community, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         return msg
 
     @staticmethod
@@ -288,14 +336,20 @@ class MessageAPI(object):
 
     @staticmethod
     def setPDU(msg, value):
-        msg.setComponentByPosition(2).getComponentByPosition(2).setComponentByType(value.getTagSet(), value, verifyConstraints=False, matchTags=False, matchConstraints=False, innerFlag=True)
+        (msg.setComponentByPosition(2)
+         .getComponentByPosition(2)
+         .setComponentByType(value.getTagSet(), value, verifyConstraints=False,
+                             matchTags=False, matchConstraints=False,
+                             innerFlag=True))
 
     def getResponse(self, reqMsg):
         rspMsg = Message()
+
         self.setDefaults(rspMsg)
         self.setVersion(rspMsg, self.getVersion(reqMsg))
         self.setCommunity(rspMsg, self.getCommunity(reqMsg))
         self.setPDU(rspMsg, apiPDU.getResponse(self.getPDU(reqMsg)))
+
         return rspMsg
 
 
diff --git a/pysnmp/proto/api/v2c.py b/pysnmp/proto/api/v2c.py
index 05de2da1..c415ca9a 100644
--- a/pysnmp/proto/api/v2c.py
+++ b/pysnmp/proto/api/v2c.py
@@ -53,7 +53,8 @@ apiVarBind = v1.apiVarBind
 
 class PDUAPI(v1.PDUAPI):
     _errorStatus = rfc1905.errorStatus.clone(0)
-    _errorIndex = univ.Integer(0).subtype(subtypeSpec=constraint.ValueRangeConstraint(0, rfc1905.max_bindings))
+    _errorIndex = univ.Integer(0).subtype(
+        subtypeSpec=constraint.ValueRangeConstraint(0, rfc1905.max_bindings))
 
     def getResponse(self, reqPDU):
         rspPDU = ResponsePDU()
@@ -86,14 +87,14 @@ class PDUAPI(v1.PDUAPI):
     def setEndOfMibError(self, pdu, errorIndex):
         varBindList = self.getVarBindList(pdu)
         varBindList[errorIndex - 1].setComponentByPosition(
-            1, rfc1905.endOfMibView, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, rfc1905.endOfMibView, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
     def setNoSuchInstanceError(self, pdu, errorIndex):
         varBindList = self.getVarBindList(pdu)
         varBindList[errorIndex - 1].setComponentByPosition(
-            1, rfc1905.noSuchInstance, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, rfc1905.noSuchInstance, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
 
 apiPDU = PDUAPI()
@@ -105,15 +106,19 @@ class BulkPDUAPI(PDUAPI):
 
     def setDefaults(self, pdu):
         PDUAPI.setDefaults(self, pdu)
+
         pdu.setComponentByPosition(
-            0, getNextRequestID(), verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, getNextRequestID(), verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            1, self._nonRepeaters, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, self._nonRepeaters, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            2, self._maxRepetitions, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._maxRepetitions, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(3)
 
     @staticmethod
@@ -152,9 +157,11 @@ class BulkPDUAPI(PDUAPI):
         if R:
             for i in range(0, len(rspVarBinds) - N, R):
                 varBindRow = rspVarBinds[:N] + rspVarBinds[N + i:N + R + i]
+
                 # ignore stray OIDs / non-rectangular table
                 if len(varBindRow) == N + R:
                     varBindTable.append(varBindRow)
+
         elif N:
             varBindTable.append(rspVarBinds[:N])
 
@@ -175,9 +182,11 @@ class TrapPDUAPI(v1.PDUAPI):
 
     def setDefaults(self, pdu):
         v1.PDUAPI.setDefaults(self, pdu)
+
         varBinds = [(self.sysUpTime, self._zeroTime),
                     # generic trap
                     (self.snmpTrapOID, self._genTrap)]
+
         self.setVarBinds(pdu, varBinds)
 
 
@@ -188,16 +197,24 @@ class MessageAPI(v1.MessageAPI):
     _version = rfc1901.version.clone(1)
 
     def setDefaults(self, msg):
-        msg.setComponentByPosition(0, self._version, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        msg.setComponentByPosition(1, self._community, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        msg.setComponentByPosition(
+            0, self._version, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        msg.setComponentByPosition(
+            1, self._community, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         return msg
 
     def getResponse(self, reqMsg):
         rspMsg = Message()
+
         self.setDefaults(rspMsg)
         self.setVersion(rspMsg, self.getVersion(reqMsg))
         self.setCommunity(rspMsg, self.getCommunity(reqMsg))
         self.setPDU(rspMsg, apiPDU.getResponse(self.getPDU(reqMsg)))
+
         return rspMsg
 
 
diff --git a/pysnmp/proto/api/verdec.py b/pysnmp/proto/api/verdec.py
index e6ec7fd9..142a68c2 100644
--- a/pysnmp/proto/api/verdec.py
+++ b/pysnmp/proto/api/verdec.py
@@ -18,13 +18,17 @@ def decodeMessageVersion(wholeMsg):
             wholeMsg, asn1Spec=univ.Sequence(),
             recursiveFlag=False, substrateFun=lambda a, b, c: (a, b[:c])
         )
+
         ver, wholeMsg = decoder.decode(
             wholeMsg, asn1Spec=univ.Integer(),
             recursiveFlag=False, substrateFun=lambda a, b, c: (a, b[:c])
         )
+
         if eoo.endOfOctets.isSameTypeWith(ver):
             raise ProtocolError('EOO at SNMP version component')
+
         return ver
 
     except PyAsn1Error as exc:
-        raise ProtocolError('Invalid BER at SNMP version component: %s' % exc)
+        raise ProtocolError('Invalid BER at SNMP version '
+                            'component: %s' % exc)
diff --git a/pysnmp/proto/cache.py b/pysnmp/proto/cache.py
index 9eae19c9..eed689ff 100644
--- a/pysnmp/proto/cache.py
+++ b/pysnmp/proto/cache.py
@@ -9,30 +9,30 @@ from pysnmp.proto import error
 
 class Cache(object):
     def __init__(self):
-        self.__cacheRepository = {}
+        self._cacheRepository = {}
 
     def add(self, index, **kwargs):
-        self.__cacheRepository[index] = kwargs
+        self._cacheRepository[index] = kwargs
         return index
 
     def pop(self, index):
-        if index in self.__cacheRepository:
-            cachedParams = self.__cacheRepository[index]
+        if index in self._cacheRepository:
+            cachedParams = self._cacheRepository[index]
         else:
             return
-        del self.__cacheRepository[index]
+        del self._cacheRepository[index]
         return cachedParams
 
     def update(self, index, **kwargs):
-        if index not in self.__cacheRepository:
+        if index not in self._cacheRepository:
             raise error.ProtocolError(
                 'Cache miss on update for %s' % kwargs
             )
-        self.__cacheRepository[index].update(kwargs)
+        self._cacheRepository[index].update(kwargs)
 
     def expire(self, cbFun, cbCtx):
-        for index, cachedParams in list(self.__cacheRepository.items()):
+        for index, cachedParams in list(self._cacheRepository.items()):
             if cbFun:
                 if cbFun(index, cachedParams, cbCtx):
-                    if index in self.__cacheRepository:
-                        del self.__cacheRepository[index]
+                    if index in self._cacheRepository:
+                        del self._cacheRepository[index]
diff --git a/pysnmp/proto/errind.py b/pysnmp/proto/errind.py
index 0c0dcb80..758a9ae1 100644
--- a/pysnmp/proto/errind.py
+++ b/pysnmp/proto/errind.py
@@ -10,30 +10,34 @@ class ErrorIndication(Exception):
     """SNMPv3 error-indication values"""
 
     def __init__(self, descr=None):
-        self.__value = self.__descr = self.__class__.__name__[0].lower() + self.__class__.__name__[1:]
+        self._value = (
+                self.__class__.__name__[0].lower() +
+                self.__class__.__name__[1:])
+        self._descr = self._value
+
         if descr:
-            self.__descr = descr
+            self._descr = descr
 
     def __eq__(self, other):
-        return self.__value == other
+        return self._value == other
 
     def __ne__(self, other):
-        return self.__value != other
+        return self._value != other
 
     def __lt__(self, other):
-        return self.__value < other
+        return self._value < other
 
     def __le__(self, other):
-        return self.__value <= other
+        return self._value <= other
 
     def __gt__(self, other):
-        return self.__value > other
+        return self._value > other
 
     def __ge__(self, other):
-        return self.__value >= other
+        return self._value >= other
 
     def __str__(self):
-        return self.__descr
+        return self._descr
 
 
 # SNMP message processing errors
@@ -42,84 +46,96 @@ class SerializationError(ErrorIndication):
     pass
 
 
-serializationError = SerializationError('SNMP message serialization error')
+serializationError = SerializationError(
+    'SNMP message serialization error')
 
 
 class DeserializationError(ErrorIndication):
     pass
 
 
-deserializationError = DeserializationError('SNMP message deserialization error')
+deserializationError = DeserializationError(
+    'SNMP message deserialization error')
 
 
 class ParseError(DeserializationError):
     pass
 
 
-parseError = ParseError('SNMP message deserialization error')
+parseError = ParseError(
+    'SNMP message deserialization error')
 
 
 class UnsupportedMsgProcessingModel(ErrorIndication):
     pass
 
 
-unsupportedMsgProcessingModel = UnsupportedMsgProcessingModel('Unknown SNMP message processing model ID encountered')
+unsupportedMsgProcessingModel = UnsupportedMsgProcessingModel(
+    'Unknown SNMP message processing model ID encountered')
 
 
 class UnknownPDUHandler(ErrorIndication):
     pass
 
 
-unknownPDUHandler = UnknownPDUHandler('Unhandled PDU type encountered')
+unknownPDUHandler = UnknownPDUHandler(
+    'Unhandled PDU type encountered')
 
 
 class UnsupportedPDUtype(ErrorIndication):
     pass
 
 
-unsupportedPDUtype = UnsupportedPDUtype('Unsupported SNMP PDU type encountered')
+unsupportedPDUtype = UnsupportedPDUtype(
+    'Unsupported SNMP PDU type encountered')
 
 
 class RequestTimedOut(ErrorIndication):
     pass
 
 
-requestTimedOut = RequestTimedOut('No SNMP response received before timeout')
+requestTimedOut = RequestTimedOut(
+    'No SNMP response received before timeout')
 
 
 class EmptyResponse(ErrorIndication):
     pass
 
 
-emptyResponse = EmptyResponse('Empty SNMP response message')
+emptyResponse = EmptyResponse(
+    'Empty SNMP response message')
 
 
 class NonReportable(ErrorIndication):
     pass
 
 
-nonReportable = NonReportable('Report PDU generation not attempted')
+nonReportable = NonReportable(
+    'Report PDU generation not attempted')
 
 
 class DataMismatch(ErrorIndication):
     pass
 
 
-dataMismatch = DataMismatch('SNMP request/response parameters mismatched')
+dataMismatch = DataMismatch(
+    'SNMP request/response parameters mismatched')
 
 
 class EngineIDMismatch(ErrorIndication):
     pass
 
 
-engineIDMismatch = EngineIDMismatch('SNMP engine ID mismatch encountered')
+engineIDMismatch = EngineIDMismatch(
+    'SNMP engine ID mismatch encountered')
 
 
 class UnknownEngineID(ErrorIndication):
     pass
 
 
-unknownEngineID = UnknownEngineID('Unknown SNMP engine ID encountered')
+unknownEngineID = UnknownEngineID(
+    'Unknown SNMP engine ID encountered')
 
 
 class TooBig(ErrorIndication):
@@ -133,14 +149,16 @@ class LoopTerminated(ErrorIndication):
     pass
 
 
-loopTerminated = LoopTerminated('Infinite SNMP entities talk terminated')
+loopTerminated = LoopTerminated(
+    'Infinite SNMP entities talk terminated')
 
 
 class InvalidMsg(ErrorIndication):
     pass
 
 
-invalidMsg = InvalidMsg('Invalid SNMP message header parameters encountered')
+invalidMsg = InvalidMsg(
+    'Invalid SNMP message header parameters encountered')
 
 
 # SNMP security modules errors
@@ -149,112 +167,128 @@ class UnknownCommunityName(ErrorIndication):
     pass
 
 
-unknownCommunityName = UnknownCommunityName('Unknown SNMP community name encountered')
+unknownCommunityName = UnknownCommunityName(
+    'Unknown SNMP community name encountered')
 
 
 class NoEncryption(ErrorIndication):
     pass
 
 
-noEncryption = NoEncryption('No encryption services configured')
+noEncryption = NoEncryption(
+    'No encryption services configured')
 
 
 class EncryptionError(ErrorIndication):
     pass
 
 
-encryptionError = EncryptionError('Ciphering services not available')
+encryptionError = EncryptionError(
+    'Ciphering services not available')
 
 
 class DecryptionError(ErrorIndication):
     pass
 
 
-decryptionError = DecryptionError('Ciphering services not available or ciphertext is broken')
+decryptionError = DecryptionError(
+    'Ciphering services not available or ciphertext is broken')
 
 
 class NoAuthentication(ErrorIndication):
     pass
 
 
-noAuthentication = NoAuthentication('No authentication services configured')
+noAuthentication = NoAuthentication(
+    'No authentication services configured')
 
 
 class AuthenticationError(ErrorIndication):
     pass
 
 
-authenticationError = AuthenticationError('Ciphering services not available or bad parameters')
+authenticationError = AuthenticationError(
+    'Ciphering services not available or bad parameters')
 
 
 class AuthenticationFailure(ErrorIndication):
     pass
 
 
-authenticationFailure = AuthenticationFailure('Authenticator mismatched')
+authenticationFailure = AuthenticationFailure(
+    'Authenticator mismatched')
 
 
 class UnsupportedAuthProtocol(ErrorIndication):
     pass
 
 
-unsupportedAuthProtocol = UnsupportedAuthProtocol('Authentication protocol is not supported')
+unsupportedAuthProtocol = UnsupportedAuthProtocol(
+    'Authentication protocol is not supported')
 
 
 class UnsupportedPrivProtocol(ErrorIndication):
     pass
 
 
-unsupportedPrivProtocol = UnsupportedPrivProtocol('Privacy protocol is not supported')
+unsupportedPrivProtocol = UnsupportedPrivProtocol(
+    'Privacy protocol is not supported')
 
 
 class UnknownSecurityName(ErrorIndication):
     pass
 
 
-unknownSecurityName = UnknownSecurityName('Unknown SNMP security name encountered')
+unknownSecurityName = UnknownSecurityName(
+    'Unknown SNMP security name encountered')
 
 
 class UnsupportedSecurityModel(ErrorIndication):
     pass
 
 
-unsupportedSecurityModel = UnsupportedSecurityModel('Unsupported SNMP security model')
+unsupportedSecurityModel = UnsupportedSecurityModel(
+    'Unsupported SNMP security model')
 
 
 class UnsupportedSecurityLevel(ErrorIndication):
     pass
 
 
-unsupportedSecurityLevel = UnsupportedSecurityLevel('Unsupported SNMP security level')
+unsupportedSecurityLevel = UnsupportedSecurityLevel(
+    'Unsupported SNMP security level')
 
 
 class NotInTimeWindow(ErrorIndication):
     pass
 
 
-notInTimeWindow = NotInTimeWindow('SNMP message timing parameters not in windows of trust')
+notInTimeWindow = NotInTimeWindow(
+    'SNMP message timing parameters not in windows of trust')
 
 
 class UnknownUserName(ErrorIndication):
     pass
 
 
-unknownUserName = UnknownUserName('Unknown USM user')
+unknownUserName = UnknownUserName(
+    'Unknown USM user')
 
 
 class WrongDigest(ErrorIndication):
     pass
 
 
-wrongDigest = WrongDigest('Wrong SNMP PDU digest')
+wrongDigest = WrongDigest(
+    'Wrong SNMP PDU digest')
 
 
 class ReportPduReceived(ErrorIndication):
     pass
 
 
-reportPduReceived = ReportPduReceived('Remote SNMP engine reported error')
+reportPduReceived = ReportPduReceived(
+    'Remote SNMP engine reported error')
 
 
 # SNMP access-control errors
@@ -263,36 +297,40 @@ class NoSuchView(ErrorIndication):
     pass
 
 
-noSuchView = NoSuchView('No such MIB view currently exists')
+noSuchView = NoSuchView(
+    'No such MIB view currently exists')
 
 
 class NoAccessEntry(ErrorIndication):
     pass
 
 
-
-noAccessEntry = NoAccessEntry('Access to MIB node denined')
+noAccessEntry = NoAccessEntry(
+    'Access to MIB node denined')
 
 
 class NoGroupName(ErrorIndication):
     pass
 
 
-noGroupName = NoGroupName('No such VACM group configured')
+noGroupName = NoGroupName(
+    'No such VACM group configured')
 
 
 class NoSuchContext(ErrorIndication):
     pass
 
 
-noSuchContext = NoSuchContext('SNMP context now found')
+noSuchContext = NoSuchContext(
+    'SNMP context now found')
 
 
 class NotInView(ErrorIndication):
     pass
 
 
-notInView = NotInView('Requested OID is out of MIB view')
+notInView = NotInView(
+    'Requested OID is out of MIB view')
 
 
 class AccessAllowed(ErrorIndication):
@@ -306,7 +344,8 @@ class OtherError(ErrorIndication):
     pass
 
 
-otherError = OtherError('Unspecified SNMP engine error occurred')
+otherError = OtherError(
+    'Unspecified SNMP engine error occurred')
 
 
 # SNMP Apps errors
@@ -315,4 +354,5 @@ class OidNotIncreasing(ErrorIndication):
     pass
 
 
-oidNotIncreasing = OidNotIncreasing('OID not increasing')
+oidNotIncreasing = OidNotIncreasing(
+    'OID not increasing')
diff --git a/pysnmp/proto/error.py b/pysnmp/proto/error.py
index 52e84642..4847bddf 100644
--- a/pysnmp/proto/error.py
+++ b/pysnmp/proto/error.py
@@ -23,8 +23,11 @@ class SnmpV3Error(ProtocolError):
 class StatusInformation(SnmpV3Error):
     def __init__(self, **kwargs):
         SnmpV3Error.__init__(self)
+
         self.__errorIndication = kwargs
-        debug.logger & (debug.FLAG_DSP | debug.FLAG_MP | debug.FLAG_SM | debug.FLAG_ACL) and debug.logger(
+
+        debug.logger & (debug.FLAG_DSP | debug.FLAG_MP |
+                        debug.FLAG_SM | debug.FLAG_ACL) and debug.logger(
             'StatusInformation: %s' % kwargs)
 
     def __str__(self):
diff --git a/pysnmp/proto/mpmod/base.py b/pysnmp/proto/mpmod/base.py
index 61b26662..835aca53 100644
--- a/pysnmp/proto/mpmod/base.py
+++ b/pysnmp/proto/mpmod/base.py
@@ -20,6 +20,7 @@ class AbstractMessageProcessingModel(object):
                                securityModel, securityName, securityLevel,
                                contextEngineId, contextName, pduVersion,
                                pdu, expectResponse, sendPduHandle):
+
         raise error.ProtocolError('method not implemented')
 
     def prepareResponseMessage(self, snmpEngine, messageProcessingModel,
@@ -27,15 +28,18 @@ class AbstractMessageProcessingModel(object):
                                contextEngineId, contextName, pduVersion,
                                pdu, maxSizeResponseScopedPDU,
                                stateReference, statusInformation):
+
         raise error.ProtocolError('method not implemented')
 
     def prepareDataElements(self, snmpEngine, transportDomain,
                             transportAddress, wholeMsg):
+
         raise error.ProtocolError('method not implemented')
 
     def releaseStateInformation(self, sendPduHandle):
         try:
             self._cache.popBySendPduHandle(sendPduHandle)
+
         except error.ProtocolError:
             pass  # XXX maybe these should all follow some scheme?
 
diff --git a/pysnmp/proto/mpmod/cache.py b/pysnmp/proto/mpmod/cache.py
index 0cb343bd..265355a4 100644
--- a/pysnmp/proto/mpmod/cache.py
+++ b/pysnmp/proto/mpmod/cache.py
@@ -27,25 +27,37 @@ class Cache(object):
 
     def pushByStateRef(self, stateReference, **msgInfo):
         if stateReference in self.__stateReferenceIndex:
-            raise error.ProtocolError('Cache dup for stateReference=%s at %s' % (stateReference, self))
+            raise error.ProtocolError(
+                'Cache dup for stateReference=%s at %s' % (stateReference, self))
+
         expireAt = self.__expirationTimer + 600
+
         self.__stateReferenceIndex[stateReference] = msgInfo, expireAt
 
         # Schedule to expire
         if expireAt not in self.__expirationQueue:
             self.__expirationQueue[expireAt] = {}
+
         if 'stateReference' not in self.__expirationQueue[expireAt]:
             self.__expirationQueue[expireAt]['stateReference'] = {}
+
         self.__expirationQueue[expireAt]['stateReference'][stateReference] = 1
 
     def popByStateRef(self, stateReference):
         if stateReference in self.__stateReferenceIndex:
             cacheInfo = self.__stateReferenceIndex[stateReference]
+
         else:
-            raise error.ProtocolError('Cache miss for stateReference=%s at %s' % (stateReference, self))
+            raise error.ProtocolError(
+                'Cache miss for stateReference=%s at '
+                '%s' % (stateReference, self))
+
         del self.__stateReferenceIndex[stateReference]
+
         cacheEntry, expireAt = cacheInfo
+
         del self.__expirationQueue[expireAt]['stateReference'][stateReference]
+
         return cacheEntry
 
     # Client mode cache handling
@@ -56,9 +68,10 @@ class Cache(object):
     def pushByMsgId(self, msgId, **msgInfo):
         if msgId in self.__msgIdIndex:
             raise error.ProtocolError(
-                'Cache dup for msgId=%s at %s' % (msgId, self)
-            )
+                'Cache dup for msgId=%s at %s' % (msgId, self))
+
         expireAt = self.__expirationTimer + 600
+
         self.__msgIdIndex[msgId] = msgInfo, expireAt
 
         self.__sendPduHandleIdx[msgInfo['sendPduHandle']] = msgId
@@ -66,22 +79,29 @@ class Cache(object):
         # Schedule to expire
         if expireAt not in self.__expirationQueue:
             self.__expirationQueue[expireAt] = {}
+
         if 'msgId' not in self.__expirationQueue[expireAt]:
             self.__expirationQueue[expireAt]['msgId'] = {}
+
         self.__expirationQueue[expireAt]['msgId'][msgId] = 1
 
     def popByMsgId(self, msgId):
         if msgId in self.__msgIdIndex:
             cacheInfo = self.__msgIdIndex[msgId]
+
         else:
             raise error.ProtocolError(
-                'Cache miss for msgId=%s at %s' % (msgId, self)
-            )
+                'Cache miss for msgId=%s at %s' % (msgId, self))
+
         msgInfo, expireAt = cacheInfo
+
         del self.__sendPduHandleIdx[msgInfo['sendPduHandle']]
         del self.__msgIdIndex[msgId]
+
         cacheEntry, expireAt = cacheInfo
+
         del self.__expirationQueue[expireAt]['msgId'][msgId]
+
         return cacheEntry
 
     def popBySendPduHandle(self, sendPduHandle):
@@ -92,11 +112,15 @@ class Cache(object):
         # Uses internal clock to expire pending messages
         if self.__expirationTimer in self.__expirationQueue:
             cacheInfo = self.__expirationQueue[self.__expirationTimer]
+
             if 'stateReference' in cacheInfo:
                 for stateReference in cacheInfo['stateReference']:
                     del self.__stateReferenceIndex[stateReference]
+
             if 'msgId' in cacheInfo:
                 for msgId in cacheInfo['msgId']:
                     del self.__msgIdIndex[msgId]
+
             del self.__expirationQueue[self.__expirationTimer]
+
         self.__expirationTimer += 1
diff --git a/pysnmp/proto/mpmod/rfc2576.py b/pysnmp/proto/mpmod/rfc2576.py
index 8bad83c2..36011619 100644
--- a/pysnmp/proto/mpmod/rfc2576.py
+++ b/pysnmp/proto/mpmod/rfc2576.py
@@ -32,9 +32,11 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                                securityModel, securityName, securityLevel,
                                contextEngineId, contextName, pduVersion,
                                pdu, expectResponse, sendPduHandle):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-        snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineId, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineId = snmpEngineId.syntax
 
         # rfc3412: 7.1.1b
@@ -42,8 +44,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             # serve unique PDU request-id
             msgID = self._cache.newMsgID()
             reqID = pdu.getComponentByPosition(0)
+
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareOutgoingMessage: PDU request-id %s replaced with unique ID %s' % (reqID, msgID))
+                'prepareOutgoingMessage: PDU request-id %s replaced with '
+                'unique ID %s' % (reqID, msgID))
 
         # rfc3412: 7.1.4
         # Since there's no SNMP engine identification in v1/2c,
@@ -56,17 +60,19 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             contextName = null
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: using contextEngineId %r contextName %r' % (contextEngineId, contextName))
+            'prepareOutgoingMessage: using contextEngineId %r contextName '
+            '%r' % (contextEngineId, contextName))
 
         # rfc3412: 7.1.6
-        scopedPDU = (contextEngineId, contextName, pdu)
+        scopedPDU = contextEngineId, contextName, pdu
 
         msg = self._snmpMsgSpec
+
         msg.setComponentByPosition(0, self.MESSAGE_PROCESSING_MODEL_ID)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # rfc3412: 7.1.7
         globalData = (msg,)
@@ -74,15 +80,15 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         k = int(securityModel)
         if k in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedSecurityModel
-            )
+                errorIndication=errind.unsupportedSecurityModel)
 
         # rfc3412: 7.1.9.a & rfc2576: 5.2.1 --> no-op
 
-        snmpEngineMaxMessageSize, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                             'snmpEngineMaxMessageSize')
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
 
         # fix unique request-id right prior PDU serialization
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
@@ -90,12 +96,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             pdu.setComponentByPosition(0, msgID)
 
         # rfc3412: 7.1.9.b
-        (securityParameters,
-         wholeMsg) = smHandler.generateRequestMsg(
+        securityParameters, wholeMsg = smHandler.generateRequestMsg(
             snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, globalData,
             snmpEngineMaxMessageSize.syntax, securityModel,
-            snmpEngineId, securityName, securityLevel, scopedPDU
-        )
+            snmpEngineId, securityName, securityLevel, scopedPDU)
 
         # return original request-id right after PDU serialization
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
@@ -105,15 +109,16 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         # rfc3412: 7.1.9.c
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             # XXX rfc bug? why stateReference should be created?
-            self._cache.pushByMsgId(int(msgID), sendPduHandle=sendPduHandle,
-                                    reqID=reqID, snmpEngineId=snmpEngineId,
-                                    securityModel=securityModel,
-                                    securityName=securityName,
-                                    securityLevel=securityLevel,
-                                    contextEngineId=contextEngineId,
-                                    contextName=contextName,
-                                    transportDomain=transportDomain,
-                                    transportAddress=transportAddress)
+            self._cache.pushByMsgId(
+                int(msgID), sendPduHandle=sendPduHandle,
+                reqID=reqID, snmpEngineId=snmpEngineId,
+                securityModel=securityModel,
+                securityName=securityName,
+                securityLevel=securityLevel,
+                contextEngineId=contextEngineId,
+                contextName=contextName,
+                transportDomain=transportDomain,
+                transportAddress=transportAddress)
 
         communityName = msg.getComponentByPosition(1)  # for observer
 
@@ -128,11 +133,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                  contextEngineId=contextEngineId,
                  contextName=contextName,
                  communityName=communityName,
-                 pdu=pdu)
-        )
+                 pdu=pdu))
+
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc2576.prepareOutgoingMessage'
-        )
+            snmpEngine, 'rfc2576.prepareOutgoingMessage')
 
         return transportDomain, transportAddress, wholeMsg
 
@@ -142,9 +146,11 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                                contextEngineId, contextName, pduVersion,
                                pdu, maxSizeResponseScopedPDU, stateReference,
                                statusInformation):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-        snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineId, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineId = snmpEngineId.syntax
 
         # rfc3412: 7.1.2.b
@@ -152,6 +158,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             raise error.StatusInformation(errorIndication=errind.nonReportable)
 
         cachedParams = self._cache.popByStateRef(stateReference)
+
         msgID = cachedParams['msgID']
         reqID = cachedParams['reqID']
         contextEngineId = cachedParams['contextEngineId']
@@ -165,7 +172,8 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         transportAddress = cachedParams['transportAddress']
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: cache read msgID %s transportDomain %s transportAddress %s by stateReference %s' % (
+            'prepareResponseMessage: cache read msgID %s transportDomain %s '
+            'transportAddress %s by stateReference %s' % (
                 msgID, transportDomain, transportAddress, stateReference))
 
         # rfc3412: 7.1.3
@@ -189,14 +197,15 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         scopedPDU = (contextEngineId, contextName, pdu)
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: using contextEngineId %r contextName %r' % (contextEngineId, contextName))
+            'prepareResponseMessage: using contextEngineId %r contextName '
+            '%r' % (contextEngineId, contextName))
 
         msg = self._snmpMsgSpec
         msg.setComponentByPosition(0, messageProcessingModel)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # att: msgId not set back to PDU as it's up to responder app
 
@@ -206,20 +215,19 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         k = int(securityModel)
         if k in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedSecurityModel
-            )
+                errorIndication=errind.unsupportedSecurityModel)
 
         # set original request-id right prior to PDU serialization
         pdu.setComponentByPosition(0, reqID)
 
         # rfc3412: 7.1.8.a
-        (securityParameters, wholeMsg) = smHandler.generateResponseMsg(
+        securityParameters, wholeMsg = smHandler.generateResponseMsg(
             snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, globalData,
             maxMessageSize, securityModel, snmpEngineId, securityName,
-            securityLevel, scopedPDU, securityStateReference
-        )
+            securityLevel, scopedPDU, securityStateReference)
 
         # recover unique request-id right after PDU serialization
         pdu.setComponentByPosition(0, msgID)
@@ -235,11 +243,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                  contextName=contextName,
                  securityEngineId=snmpEngineId,
                  communityName=msg.getComponentByPosition(1),
-                 pdu=pdu)
-        )
+                 pdu=pdu))
+
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc2576.prepareResponseMessage'
-        )
+            snmpEngine, 'rfc2576.prepareResponseMessage')
 
         return transportDomain, transportAddress, wholeMsg
 
@@ -247,12 +254,14 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
 
     def prepareDataElements(self, snmpEngine, transportDomain,
                             transportAddress, wholeMsg):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
         # rfc3412: 7.2.2
         msg, restOfWholeMsg = decoder.decode(wholeMsg, asn1Spec=self._snmpMsgSpec)
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareDataElements: %s' % (msg.prettyPrint(),))
 
         if eoo.endOfOctets.isSameTypeWith(msg):
             raise error.StatusInformation(errorIndication=errind.parseError)
@@ -261,8 +270,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         msgVersion = msg.getComponentByPosition(0)
 
         # rfc2576: 5.2.1
-        snmpEngineMaxMessageSize, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
         communityName = msg.getComponentByPosition(1)
+
         # transportDomain identifies local endpoint
         securityParameters = (communityName, (transportDomain, transportAddress))
         messageProcessingModel = int(msg.getComponentByPosition(0))
@@ -293,7 +304,8 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             )
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: SM returned securityEngineId %r securityName %r' % (securityEngineId, securityName))
+                'prepareDataElements: SM returned securityEngineId %r '
+                'securityName %r' % (securityEngineId, securityName))
 
         except error.StatusInformation as exc:
             statusInformation = exc
@@ -305,11 +317,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      securityModel=securityModel,
                      securityLevel=securityLevel,
                      securityParameters=securityParameters,
-                     statusInformation=statusInformation)
-            )
+                     statusInformation=statusInformation))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:sm-failure'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:sm-failure')
 
             raise
 
@@ -332,6 +343,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             # 7.2.10a
             try:
                 cachedReqParams = self._cache.popByMsgId(int(msgID))
+
             except error.ProtocolError:
                 smHandler.releaseStateInformation(securityStateReference)
                 raise error.StatusInformation(errorIndication=errind.dataMismatch)
@@ -340,11 +352,12 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             pdu.setComponentByPosition(0, cachedReqParams['reqID'])
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: unique PDU request-id %s replaced with original ID %s' % (
-                    msgID, cachedReqParams['reqID']))
+                'prepareDataElements: unique PDU request-id %s replaced with '
+                'original ID %s' % (msgID, cachedReqParams['reqID']))
 
             # 7.2.10b
             sendPduHandle = cachedReqParams['sendPduHandle']
+
         else:
             sendPduHandle = None
 
@@ -363,7 +376,9 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                     securityLevel != cachedReqParams['securityLevel'] or
                     contextEngineId != cachedReqParams['contextEngineId'] or
                     contextName != cachedReqParams['contextName']):
+
                 smHandler.releaseStateInformation(securityStateReference)
+
                 raise error.StatusInformation(errorIndication=errind.dataMismatch)
 
             stateReference = None
@@ -379,11 +394,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      contextName=contextName,
                      securityEngineId=securityEngineId,
                      communityName=communityName,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:response'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:response')
 
             # rfc3412: 7.2.12c
             smHandler.releaseStateInformation(securityStateReference)
@@ -401,19 +415,23 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             reqID = pdu.getComponentByPosition(0)
             msgID = self._cache.newMsgID()
             pdu.setComponentByPosition(0, msgID)
+
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: received PDU request-id %s replaced with unique ID %s' % (reqID, msgID))
+                'prepareDataElements: received PDU request-id %s replaced with '
+                'unique ID %s' % (reqID, msgID))
 
             # rfc3412: 7.2.13a
-            snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+            snmpEngineId, = mibBuilder.importSymbols(
+                '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+
             if securityEngineId != snmpEngineId.syntax:
                 smHandler.releaseStateInformation(securityStateReference)
                 raise error.StatusInformation(
-                    errorIndication=errind.engineIDMismatch
-                )
+                    errorIndication=errind.engineIDMismatch)
 
             # rfc3412: 7.2.13b
             stateReference = self._cache.newStateReference()
+
             self._cache.pushByStateRef(
                 stateReference, msgVersion=messageProcessingModel,
                 msgID=msgID, reqID=reqID, contextEngineId=contextEngineId,
@@ -437,14 +455,14 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      contextName=contextName,
                      securityEngineId=securityEngineId,
                      communityName=communityName,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:confirmed'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:confirmed')
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: cached by new stateReference %s' % stateReference)
+                'prepareDataElements: cached by new stateReference '
+                '%s' % stateReference)
 
             # rfc3412: 7.2.13c
             return (messageProcessingModel, securityModel, securityName,
@@ -469,11 +487,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      contextName=contextName,
                      securityEngineId=securityEngineId,
                      communityName=communityName,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:unconfirmed'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:unconfirmed')
 
             # This is not specified explicitly in RFC
             smHandler.releaseStateInformation(securityStateReference)
@@ -485,6 +502,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                     stateReference)
 
         smHandler.releaseStateInformation(securityStateReference)
+
         raise error.StatusInformation(errorIndication=errind.unsupportedPDUtype)
 
 
diff --git a/pysnmp/proto/mpmod/rfc3412.py b/pysnmp/proto/mpmod/rfc3412.py
index 6ff9fa8d..20852db6 100644
--- a/pysnmp/proto/mpmod/rfc3412.py
+++ b/pysnmp/proto/mpmod/rfc3412.py
@@ -30,49 +30,53 @@ class ScopedPDU(univ.Sequence):
     componentType = namedtype.NamedTypes(
         namedtype.NamedType('contextEngineId', univ.OctetString()),
         namedtype.NamedType('contextName', univ.OctetString()),
-        namedtype.NamedType('data', rfc1905.PDUs())
-    )
+        namedtype.NamedType('data', rfc1905.PDUs()))
 
 
 class ScopedPduData(univ.Choice):
     componentType = namedtype.NamedTypes(
         namedtype.NamedType('plaintext', ScopedPDU()),
-        namedtype.NamedType('encryptedPDU', univ.OctetString()),
-    )
+        namedtype.NamedType('encryptedPDU', univ.OctetString()))
 
 
 class HeaderData(univ.Sequence):
     componentType = namedtype.NamedTypes(
-        namedtype.NamedType('msgID',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
-        namedtype.NamedType('msgMaxSize',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(484, 2147483647))),
-        namedtype.NamedType('msgFlags', univ.OctetString().subtype(subtypeSpec=constraint.ValueSizeConstraint(1, 1))),
+        namedtype.NamedType(
+            'msgID', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgMaxSize', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(484, 2147483647))),
+        namedtype.NamedType(
+            'msgFlags', univ.OctetString().subtype(
+                subtypeSpec=constraint.ValueSizeConstraint(1, 1))),
         # NOTE (etingof): constrain SNMPv3 message to only USM+ security models
         # because SNMPv1/v2c seems incompatible in pysnmp implementation, not sure
         # if it's intended by the SNMP standard at all...
-        namedtype.NamedType('msgSecurityModel',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(3, 2147483647)))
-    )
+        namedtype.NamedType(
+            'msgSecurityModel', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(3, 2147483647))))
 
 
 class SNMPv3Message(univ.Sequence):
     componentType = namedtype.NamedTypes(
-        namedtype.NamedType('msgVersion',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgVersion', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
         namedtype.NamedType('msgGlobalData', HeaderData()),
         namedtype.NamedType('msgSecurityParameters', univ.OctetString()),
-        namedtype.NamedType('msgData', ScopedPduData())
-    )
+        namedtype.NamedType('msgData', ScopedPduData()))
 
 
 # XXX move somewhere?
-_snmpErrors = {(1, 3, 6, 1, 6, 3, 15, 1, 1, 1, 0): errind.unsupportedSecurityLevel,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 2, 0): errind.notInTimeWindow,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 3, 0): errind.unknownUserName,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 4, 0): errind.unknownEngineID,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 5, 0): errind.wrongDigest,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 6, 0): errind.decryptionError}
+_snmpErrors = {
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 1, 0): errind.unsupportedSecurityLevel,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 2, 0): errind.notInTimeWindow,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 3, 0): errind.unknownUserName,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 4, 0): errind.unknownEngineID,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 5, 0): errind.wrongDigest,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 6, 0): errind.decryptionError
+}
 
 
 class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
@@ -80,26 +84,28 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
     SNMP_MSG_SPEC = SNMPv3Message
 
     _emptyStr = univ.OctetString('')
-    _msgFlags = {0: univ.OctetString('\x00'),
-                 1: univ.OctetString('\x01'),
-                 3: univ.OctetString('\x03'),
-                 4: univ.OctetString('\x04'),
-                 5: univ.OctetString('\x05'),
-                 7: univ.OctetString('\x07')}
+    _msgFlags = {
+        0: univ.OctetString('\x00'),
+        1: univ.OctetString('\x01'),
+        3: univ.OctetString('\x03'),
+        4: univ.OctetString('\x04'),
+        5: univ.OctetString('\x05'),
+        7: univ.OctetString('\x07')
+    }
 
     def __init__(self):
         AbstractMessageProcessingModel.__init__(self)
-        self.__scopedPDU = ScopedPDU()
-        self.__engineIdCache = {}
-        self.__engineIdCacheExpQueue = {}
-        self.__expirationTimer = 0
+        self._scopedPDU = ScopedPDU()
+        self._engineIdCache = {}
+        self._engineIdCacheExpQueue = {}
+        self._expirationTimer = 0
 
     def getPeerEngineInfo(self, transportDomain, transportAddress):
         k = transportDomain, transportAddress
-        if k in self.__engineIdCache:
-            return (self.__engineIdCache[k]['securityEngineId'],
-                    self.__engineIdCache[k]['contextEngineId'],
-                    self.__engineIdCache[k]['contextName'])
+        if k in self._engineIdCache:
+            return (self._engineIdCache[k]['securityEngineId'],
+                    self._engineIdCache[k]['contextEngineId'],
+                    self._engineIdCache[k]['contextName'])
         else:
             return None, None, None
 
@@ -109,29 +115,35 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                                securityModel, securityName, securityLevel,
                                contextEngineId, contextName, pduVersion,
                                pdu, expectResponse, sendPduHandle):
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                              'snmpEngineID')
+
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineID = snmpEngineID.syntax
 
         # 7.1.1b
         msgID = self._cache.newMsgID()
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareOutgoingMessage: new msgID %s' % msgID)
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareOutgoingMessage: new msgID %s' % msgID)
+
+        k = transportDomain, transportAddress
+        if k in self._engineIdCache:
+            peerSnmpEngineData = self._engineIdCache[k]
 
-        k = (transportDomain, transportAddress)
-        if k in self.__engineIdCache:
-            peerSnmpEngineData = self.__engineIdCache[k]
         else:
             peerSnmpEngineData = None
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: peer SNMP engine data %s for transport %s, address %s' % (
-                peerSnmpEngineData, transportDomain, transportAddress))
+            'prepareOutgoingMessage: peer SNMP engine data %s '
+            'for transport %s, address '
+            '%s' % (peerSnmpEngineData, transportDomain, transportAddress))
 
         # 7.1.4
         if contextEngineId is None:
             if peerSnmpEngineData is None:
                 contextEngineId = snmpEngineID
+
             else:
                 contextEngineId = peerSnmpEngineData['contextEngineId']
                 # Defaulting contextEngineID to securityEngineId should
@@ -144,88 +156,98 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             contextName = self._emptyStr
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: using contextEngineId %r, contextName %r' % (contextEngineId, contextName))
+            'prepareOutgoingMessage: using contextEngineId %r, contextName '
+            '%r' % (contextEngineId, contextName))
 
         # 7.1.6
-        scopedPDU = self.__scopedPDU
+        scopedPDU = self._scopedPDU
         scopedPDU.setComponentByPosition(0, contextEngineId)
         scopedPDU.setComponentByPosition(1, contextName)
         scopedPDU.setComponentByPosition(2)
         scopedPDU.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 7.1.7
         msg = self._snmpMsgSpec
 
         # 7.1.7a
         msg.setComponentByPosition(
-            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
+
         headerData = msg.setComponentByPosition(1).getComponentByPosition(1)
 
         # 7.1.7b
-        headerData.setComponentByPosition(0, msgID, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        headerData.setComponentByPosition(
+            0, msgID, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        snmpEngineMaxMessageSize, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
             '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
 
         # 7.1.7c
         # XXX need to coerce MIB value as it has incompatible constraints set
         headerData.setComponentByPosition(
-            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         # 7.1.7d
         msgFlags = 0
         if securityLevel == 1:
             pass
+
         elif securityLevel == 2:
             msgFlags |= 0x01
+
         elif securityLevel == 3:
             msgFlags |= 0x03
+
         else:
             raise error.ProtocolError(
-                'Unknown securityLevel %s' % securityLevel
-            )
+                'Unknown securityLevel %s' % securityLevel)
 
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             msgFlags |= 0x04
 
         headerData.setComponentByPosition(
-            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._msgFlags[msgFlags], verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         # 7.1.7e
         # XXX need to coerce MIB value as it has incompatible constraints set
         headerData.setComponentByPosition(3, int(securityModel))
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareOutgoingMessage: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareOutgoingMessage: %s' % (msg.prettyPrint(),))
 
         if securityModel in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[securityModel]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedSecurityModel
-            )
+                errorIndication=errind.unsupportedSecurityModel)
 
         # 7.1.9.a
         if pdu.tagSet in rfc3411.UNCONFIRMED_CLASS_PDUS:
             securityEngineId = snmpEngineID
+
         else:
             if peerSnmpEngineData is None:
                 # Force engineID discovery (rfc3414, 4)
                 securityEngineId = securityName = self._emptyStr
                 securityLevel = 1
+
                 # Clear possible auth&priv flags
                 headerData.setComponentByPosition(
-                    2, self._msgFlags[msgFlags & 0xfc], verifyConstraints=False, matchTags=False, matchConstraints=False
-                )
+                    2, self._msgFlags[msgFlags & 0xfc], verifyConstraints=False,
+                    matchTags=False, matchConstraints=False)
+
                 # XXX
-                scopedPDU = self.__scopedPDU
+                scopedPDU = self._scopedPDU
                 scopedPDU.setComponentByPosition(
-                    0, self._emptyStr, verifyConstraints=False, matchTags=False, matchConstraints=False
-                )
+                    0, self._emptyStr, verifyConstraints=False, matchTags=False,
+                    matchConstraints=False)
                 scopedPDU.setComponentByPosition(1, contextName)
                 scopedPDU.setComponentByPosition(2)
 
@@ -234,19 +256,22 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                 pMod.apiPDU.setDefaults(emptyPdu)
 
                 scopedPDU.getComponentByPosition(2).setComponentByType(
-                    emptyPdu.tagSet, emptyPdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-                )
-                debug.logger & debug.FLAG_MP and debug.logger('prepareOutgoingMessage: force engineID discovery')
+                    emptyPdu.tagSet, emptyPdu, verifyConstraints=False,
+                    matchTags=False, matchConstraints=False)
+
+                debug.logger & debug.FLAG_MP and debug.logger(
+                    'prepareOutgoingMessage: force engineID discovery')
+
             else:
                 securityEngineId = peerSnmpEngineData['securityEngineId']
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: securityModel %r, securityEngineId %r, securityName %r, securityLevel %r' % (
-                securityModel, securityEngineId, securityName, securityLevel))
+            'prepareOutgoingMessage: securityModel %r, securityEngineId %r, '
+            'securityName %r, securityLevel '
+            '%r' % (securityModel, securityEngineId, securityName, securityLevel))
 
         # 7.1.9.b
-        (securityParameters,
-         wholeMsg) = smHandler.generateRequestMsg(
+        securityParameters, wholeMsg = smHandler.generateRequestMsg(
             snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, msg,
             snmpEngineMaxMessageSize.syntax, securityModel,
             securityEngineId, securityName, securityLevel, scopedPDU
@@ -259,15 +284,16 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         # 7.1.9.c
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             # XXX rfc bug? why stateReference should be created?
-            self._cache.pushByMsgId(msgID, sendPduHandle=sendPduHandle,
-                                    msgID=msgID, snmpEngineID=snmpEngineID,
-                                    securityModel=securityModel,
-                                    securityName=securityName,
-                                    securityLevel=securityLevel,
-                                    contextEngineId=contextEngineId,
-                                    contextName=contextName,
-                                    transportDomain=transportDomain,
-                                    transportAddress=transportAddress)
+            self._cache.pushByMsgId(
+                msgID, sendPduHandle=sendPduHandle,
+                msgID=msgID, snmpEngineID=snmpEngineID,
+                securityModel=securityModel,
+                securityName=securityName,
+                securityLevel=securityLevel,
+                contextEngineId=contextEngineId,
+                contextName=contextName,
+                transportDomain=transportDomain,
+                transportAddress=transportAddress)
 
         snmpEngine.observer.storeExecutionContext(
             snmpEngine, 'rfc3412.prepareOutgoingMessage',
@@ -292,7 +318,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                                contextEngineId, contextName, pduVersion,
                                pdu, maxSizeResponseScopedPDU, stateReference,
                                statusInformation):
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineID = snmpEngineID.syntax
 
         # 7.1.2.b
@@ -309,13 +338,15 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         transportDomain = cachedParams['transportDomain']
         transportAddress = cachedParams['transportAddress']
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareResponseMessage: stateReference %s' % stateReference)
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareResponseMessage: stateReference %s' % stateReference)
 
         # 7.1.3
         if statusInformation is not None and 'oid' in statusInformation:
             # 7.1.3a
             if pdu is None:
                 pduType = None
+
             else:
                 requestID = pdu.getComponentByPosition(0)
                 pduType = pdu.tagSet
@@ -325,16 +356,18 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     pduType is not None and
                     pduType not in rfc3411.CONFIRMED_CLASS_PDUS):
                 raise error.StatusInformation(
-                    errorIndication=errind.loopTerminated
-                )
+                    errorIndication=errind.loopTerminated)
 
             # 7.1.3c
             reportPDU = rfc1905.ReportPDU()
-            pMod.apiPDU.setVarBinds(reportPDU, ((statusInformation['oid'], statusInformation['val']),))
+            pMod.apiPDU.setVarBinds(
+                reportPDU, ((statusInformation['oid'], statusInformation['val']),))
             pMod.apiPDU.setErrorStatus(reportPDU, 0)
             pMod.apiPDU.setErrorIndex(reportPDU, 0)
+
             if pdu is None:
                 pMod.apiPDU.setRequestID(reportPDU, 0)
+
             else:
                 # noinspection PyUnboundLocalVariable
                 pMod.apiPDU.setRequestID(reportPDU, requestID)
@@ -342,18 +375,21 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             # 7.1.3d.1
             if 'securityLevel' in statusInformation:
                 securityLevel = statusInformation['securityLevel']
+
             else:
                 securityLevel = 1
 
             # 7.1.3d.2
             if 'contextEngineId' in statusInformation:
                 contextEngineId = statusInformation['contextEngineId']
+
             else:
                 contextEngineId = snmpEngineID
 
             # 7.1.3d.3
             if 'contextName' in statusInformation:
                 contextName = statusInformation['contextName']
+
             else:
                 contextName = ""
 
@@ -361,7 +397,8 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             pdu = reportPDU
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareResponseMessage: prepare report PDU for statusInformation %s' % statusInformation)
+                'prepareResponseMessage: prepare report PDU for '
+                'statusInformation %s' % statusInformation)
         # 7.1.4
         if not contextEngineId:
             contextEngineId = snmpEngineID  # XXX impl-dep manner
@@ -371,47 +408,54 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             contextName = self._emptyStr
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: using contextEngineId %r, contextName %r' % (contextEngineId, contextName))
+            'prepareResponseMessage: using contextEngineId %r, contextName '
+            '%r' % (contextEngineId, contextName))
 
         # 7.1.6
-        scopedPDU = self.__scopedPDU
+        scopedPDU = self._scopedPDU
         scopedPDU.setComponentByPosition(0, contextEngineId)
         scopedPDU.setComponentByPosition(1, contextName)
         scopedPDU.setComponentByPosition(2)
         scopedPDU.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 7.1.7
         msg = self._snmpMsgSpec
 
         # 7.1.7a
         msg.setComponentByPosition(
-            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         headerData = msg.setComponentByPosition(1).getComponentByPosition(1)
 
         # 7.1.7b
-        headerData.setComponentByPosition(0, msgID, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        headerData.setComponentByPosition(
+            0, msgID, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        snmpEngineMaxMessageSize, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
             '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
 
         # 7.1.7c
         # XXX need to coerce MIB value as it has incompatible constraints set
         headerData.setComponentByPosition(
-            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         # 7.1.7d
         msgFlags = 0
+
         if securityLevel == 1:
             pass
+
         elif securityLevel == 2:
             msgFlags |= 0x01
+
         elif securityLevel == 3:
             msgFlags |= 0x03
+
         else:
             raise error.ProtocolError('Unknown securityLevel %s' % securityLevel)
 
@@ -419,39 +463,43 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             msgFlags |= 0x04
 
         headerData.setComponentByPosition(
-            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 7.1.7e
         headerData.setComponentByPosition(
-            3, securityModel, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            3, securityModel, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareResponseMessage: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareResponseMessage: %s' % (msg.prettyPrint(),))
 
         if securityModel in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[securityModel]
+
         else:
-            raise error.StatusInformation(errorIndication=errind.unsupportedSecurityModel)
+            raise error.StatusInformation(
+                errorIndication=errind.unsupportedSecurityModel)
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: securityModel %r, securityEngineId %r, securityName %r, securityLevel %r' % (
+            'prepareResponseMessage: securityModel %r, securityEngineId %r, '
+            'securityName %r, securityLevel %r' % (
                 securityModel, snmpEngineID, securityName, securityLevel))
 
         # 7.1.8a
         try:
-            (securityParameters,
-             wholeMsg) = smHandler.generateResponseMsg(
+            securityParameters, wholeMsg = smHandler.generateResponseMsg(
                 snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, msg,
                 snmpEngineMaxMessageSize.syntax, securityModel,
                 snmpEngineID, securityName, securityLevel, scopedPDU,
-                securityStateReference
-            )
+                securityStateReference)
+
         except error.StatusInformation:
             # 7.1.8.b
             raise
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareResponseMessage: SM finished')
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareResponseMessage: SM finished')
 
         # Message size constraint verification
         if len(wholeMsg) > min(snmpEngineMaxMessageSize.syntax, maxMessageSize):
@@ -468,11 +516,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                  contextEngineId=contextEngineId,
                  contextName=contextName,
                  securityEngineId=snmpEngineID,
-                 pdu=pdu)
-        )
+                 pdu=pdu))
+
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc3412.prepareResponseMessage'
-        )
+            snmpEngine, 'rfc3412.prepareResponseMessage')
 
         return transportDomain, transportAddress, wholeMsg
 
@@ -483,11 +530,14 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         # 7.2.2
         msg, restOfwholeMsg = decoder.decode(wholeMsg, asn1Spec=self._snmpMsgSpec)
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareDataElements: %s' % (msg.prettyPrint(),))
 
         if eoo.endOfOctets.isSameTypeWith(msg):
             raise error.StatusInformation(errorIndication=errind.parseError)
 
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
         # 7.2.3
         headerData = msg.getComponentByPosition(1)
         msgVersion = messageProcessingModel = msg.getComponentByPosition(0)
@@ -498,12 +548,12 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         securityParameters = msg.getComponentByPosition(2)
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareDataElements: msg data msgVersion %s msgID %s securityModel %s' % (
-                msgVersion, msgID, securityModel))
+            'prepareDataElements: msg data msgVersion %s msgID %s '
+            'securityModel %s' % (msgVersion, msgID, securityModel))
 
         # 7.2.4
         if securityModel not in snmpEngine.securityModels:
-            snmpUnknownSecurityModels, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+            snmpUnknownSecurityModels, = mibBuilder.importSymbols(
                 '__SNMP-MPD-MIB', 'snmpUnknownSecurityModels')
             snmpUnknownSecurityModels.syntax += 1
             raise error.StatusInformation(errorIndication=errind.unsupportedSecurityModel)
@@ -511,22 +561,28 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         # 7.2.5
         if msgFlags & 0x03 == 0x00:
             securityLevel = 1
+
         elif (msgFlags & 0x03) == 0x01:
             securityLevel = 2
+
         elif (msgFlags & 0x03) == 0x03:
             securityLevel = 3
+
         else:
-            snmpInvalidMsgs, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-MPD-MIB', 'snmpInvalidMsgs')
+            snmpInvalidMsgs, = mibBuilder.importSymbols(
+                '__SNMP-MPD-MIB', 'snmpInvalidMsgs')
             snmpInvalidMsgs.syntax += 1
             raise error.StatusInformation(errorIndication=errind.invalidMsg)
 
         if msgFlags & 0x04:
             reportableFlag = 1
+
         else:
             reportableFlag = 0
 
         # 7.2.6
         smHandler = snmpEngine.securityModels[securityModel]
+
         try:
             (securityEngineId,
              securityName,
@@ -535,15 +591,17 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
              securityStateReference) = smHandler.processIncomingMsg(
                 snmpEngine, messageProcessingModel, maxMessageSize,
                 securityParameters, securityModel, securityLevel,
-                wholeMsg, msg
-            )
-            debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: SM succeeded')
+                wholeMsg, msg)
+
+            debug.logger & debug.FLAG_MP and debug.logger(
+                'prepareDataElements: SM succeeded')
 
         except error.StatusInformation as exc:
             statusInformation = exc
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: SM failed, statusInformation %s' % statusInformation)
+                'prepareDataElements: SM failed, statusInformation '
+                '%s' % statusInformation)
 
             snmpEngine.observer.storeExecutionContext(
                 snmpEngine, 'rfc3412.prepareDataElements:sm-failure',
@@ -552,11 +610,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      securityModel=securityModel,
                      securityLevel=securityLevel,
                      securityParameters=securityParameters,
-                     statusInformation=statusInformation)
-            )
+                     statusInformation=statusInformation))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:sm-failure'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:sm-failure')
 
             if 'errorIndication' in statusInformation:
                 # 7.2.6a
@@ -565,16 +622,20 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     securityStateReference = statusInformation['securityStateReference']
                     contextEngineId = statusInformation['contextEngineId']
                     contextName = statusInformation['contextName']
+
                     if 'scopedPDU' in statusInformation:
                         scopedPDU = statusInformation['scopedPDU']
                         pdu = scopedPDU.getComponentByPosition(2).getComponent()
+
                     else:
                         pdu = None
+
                     maxSizeResponseScopedPDU = statusInformation['maxSizeResponseScopedPDU']
                     securityName = None  # XXX secmod cache used
 
                     # 7.2.6a2
                     stateReference = self._cache.newStateReference()
+
                     self._cache.pushByStateRef(
                         stateReference, msgVersion=messageProcessingModel,
                         msgID=msgID, contextEngineId=contextEngineId,
@@ -585,8 +646,7 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                         msgMaxSize=maxMessageSize,
                         maxSizeResponseScopedPDU=maxSizeResponseScopedPDU,
                         transportDomain=transportDomain,
-                        transportAddress=transportAddress
-                    )
+                        transportAddress=transportAddress)
 
                     # 7.2.6a3
                     try:
@@ -594,16 +654,18 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                             snmpEngine, 3, securityModel, securityName,
                             securityLevel, contextEngineId, contextName,
                             1, pdu, maxSizeResponseScopedPDU, stateReference,
-                            statusInformation
-                        )
+                            statusInformation)
+
                     except error.StatusInformation:
                         pass
 
-                    debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: error reported')
+                    debug.logger & debug.FLAG_MP and debug.logger(
+                        'prepareDataElements: error reported')
 
             # 7.2.6b
             if sys.version_info[0] <= 2:
                 raise statusInformation
+
             else:
                 origTraceback = sys.exc_info()[2]
 
@@ -616,31 +678,36 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     del origTraceback
         else:
             # Sniff for engineIdCache
-            k = (transportDomain, transportAddress)
-            if k not in self.__engineIdCache:
+            k = transportDomain, transportAddress
+            if k not in self._engineIdCache:
                 contextEngineId = scopedPDU[0]
                 contextName = scopedPDU[1]
+
                 pdus = scopedPDU[2]
                 pdu = pdus.getComponent()
+
                 # Here we assume that authentic/default EngineIDs
                 # come only in the course of engine-to-engine communication.
                 if pdu.tagSet in rfc3411.INTERNAL_CLASS_PDUS:
-                    self.__engineIdCache[k] = {
+                    self._engineIdCache[k] = {
                         'securityEngineId': securityEngineId,
                         'contextEngineId': contextEngineId,
                         'contextName': contextName
                     }
 
-                    expireAt = int(self.__expirationTimer + 300 / snmpEngine.transportDispatcher.getTimerResolution())
-                    if expireAt not in self.__engineIdCacheExpQueue:
-                        self.__engineIdCacheExpQueue[expireAt] = []
-                    self.__engineIdCacheExpQueue[expireAt].append(k)
+                    timerResolution = snmpEngine.transportDispatcher.getTimerResolution()
+                    expireAt = int(self._expirationTimer + 300 / timerResolution)
+
+                    if expireAt not in self._engineIdCacheExpQueue:
+                        self._engineIdCacheExpQueue[expireAt] = []
+
+                    self._engineIdCacheExpQueue[expireAt].append(k)
 
                     debug.logger & debug.FLAG_MP and debug.logger(
                         'prepareDataElements: cache securityEngineId %r for %r %r' % (
                             securityEngineId, transportDomain, transportAddress))
 
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineID = snmpEngineID.syntax
 
         # 7.2.7 XXX PDU would be parsed here?
@@ -662,33 +729,39 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             # 7.2.10a
             try:
                 cachedReqParams = self._cache.popByMsgId(msgID)
+
             except error.ProtocolError:
                 smHandler.releaseStateInformation(securityStateReference)
-                raise error.StatusInformation(
-                    errorIndication=errind.dataMismatch
-                )
+                raise error.StatusInformation(errorIndication=errind.dataMismatch)
+
             # 7.2.10b
             sendPduHandle = cachedReqParams['sendPduHandle']
+
         else:
             sendPduHandle = None
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareDataElements: using sendPduHandle %s for msgID %s' % (sendPduHandle, msgID))
+            'prepareDataElements: using sendPduHandle %s for msgID '
+            '%s' % (sendPduHandle, msgID))
 
         # 7.2.11
         if pduType in rfc3411.INTERNAL_CLASS_PDUS:
             # 7.2.11a
             varBinds = pMod.apiPDU.getVarBinds(pdu)
+
             if varBinds:
+                errorIndication = _snmpErrors.get(
+                    varBinds[0][0],
+                    errind.ReportPduReceived(varBinds[0][0].prettyPrint()))
+
                 statusInformation = error.StatusInformation(
-                    errorIndication=_snmpErrors.get(varBinds[0][0], errind.ReportPduReceived(varBinds[0][0].prettyPrint())),
+                    errorIndication=errorIndication,
                     oid=varBinds[0][0], val=varBinds[0][1],
-                    sendPduHandle=sendPduHandle
-                )
+                    sendPduHandle=sendPduHandle)
+
             else:
                 statusInformation = error.StatusInformation(
-                    sendPduHandle=sendPduHandle
-                )
+                    sendPduHandle=sendPduHandle)
 
             # 7.2.11b (incomplete implementation)
 
@@ -702,11 +775,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:internal'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:internal')
 
             # 7.2.11c
             smHandler.releaseStateInformation(securityStateReference)
@@ -730,10 +802,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     securityLevel != cachedReqParams['securityLevel'] or
                     contextEngineId != cachedReqParams['contextEngineId'] or
                     contextName != cachedReqParams['contextName']):
+
                 smHandler.releaseStateInformation(securityStateReference)
-                raise error.StatusInformation(
-                    errorIndication=errind.dataMismatch
-                )
+
+                raise error.StatusInformation(errorIndication=errind.dataMismatch)
 
             snmpEngine.observer.storeExecutionContext(
                 snmpEngine, 'rfc3412.prepareDataElements:response',
@@ -745,11 +817,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:response'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:response')
 
             # 7.2.12c
             smHandler.releaseStateInformation(securityStateReference)
@@ -768,11 +839,11 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             if securityEngineId != snmpEngineID:
                 smHandler.releaseStateInformation(securityStateReference)
                 raise error.StatusInformation(
-                    errorIndication=errind.engineIDMismatch
-                )
+                    errorIndication=errind.engineIDMismatch)
 
             # 7.2.13b
             stateReference = self._cache.newStateReference()
+
             self._cache.pushByStateRef(
                 stateReference, msgVersion=messageProcessingModel,
                 msgID=msgID, contextEngineId=contextEngineId,
@@ -782,10 +853,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                 reportableFlag=reportableFlag, msgMaxSize=maxMessageSize,
                 maxSizeResponseScopedPDU=maxSizeResponseScopedPDU,
                 transportDomain=transportDomain,
-                transportAddress=transportAddress
-            )
+                transportAddress=transportAddress)
 
-            debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: new stateReference %s' % stateReference)
+            debug.logger & debug.FLAG_MP and debug.logger(
+                'prepareDataElements: new stateReference %s' % stateReference)
 
             snmpEngine.observer.storeExecutionContext(
                 snmpEngine, 'rfc3412.prepareDataElements:confirmed',
@@ -797,11 +868,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:confirmed'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:confirmed')
 
             # 7.2.13c
             return (messageProcessingModel, securityModel, securityName,
@@ -812,6 +882,7 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
 
         # 7.2.14
         if pduType in rfc3411.UNCONFIRMED_CLASS_PDUS:
+
             # Pass new stateReference to let app browse request details
             stateReference = self._cache.newStateReference()
 
@@ -825,11 +896,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed')
 
             # This is not specified explicitly in RFC
             smHandler.releaseStateInformation(securityStateReference)
@@ -841,18 +911,22 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     stateReference)
 
         smHandler.releaseStateInformation(securityStateReference)
-        raise error.StatusInformation(
-            errorIndication=errind.unsupportedPDUtype
-        )
 
-    def __expireEnginesInfo(self):
-        if self.__expirationTimer in self.__engineIdCacheExpQueue:
-            for engineKey in self.__engineIdCacheExpQueue[self.__expirationTimer]:
-                del self.__engineIdCache[engineKey]
-                debug.logger & debug.FLAG_MP and debug.logger('__expireEnginesInfo: expiring %r' % (engineKey,))
-            del self.__engineIdCacheExpQueue[self.__expirationTimer]
-        self.__expirationTimer += 1
+        raise error.StatusInformation(errorIndication=errind.unsupportedPDUtype)
+
+    def _expireEnginesInfo(self):
+        if self._expirationTimer in self._engineIdCacheExpQueue:
+
+            for engineKey in self._engineIdCacheExpQueue[self._expirationTimer]:
+                del self._engineIdCache[engineKey]
+
+                debug.logger & debug.FLAG_MP and debug.logger(
+                    '__expireEnginesInfo: expiring %r' % (engineKey,))
+
+            del self._engineIdCacheExpQueue[self._expirationTimer]
+
+        self._expirationTimer += 1
 
     def receiveTimerTick(self, snmpEngine, timeNow):
-        self.__expireEnginesInfo()
+        self._expireEnginesInfo()
         AbstractMessageProcessingModel.receiveTimerTick(self, snmpEngine, timeNow)
diff --git a/pysnmp/proto/proxy/rfc2576.py b/pysnmp/proto/proxy/rfc2576.py
index 359a3b4f..de5a5fdb 100644
--- a/pysnmp/proto/proxy/rfc2576.py
+++ b/pysnmp/proto/proxy/rfc2576.py
@@ -102,7 +102,8 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
     pduType = v1Pdu.tagSet
     v2Pdu = V1_TO_V2_PDU_MAP[pduType].clone()
 
-    debug.logger & debug.FLAG_PRX and debug.logger('v1ToV2: v1Pdu %s' % v1Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v1ToV2: v1Pdu %s' % v1Pdu.prettyPrint())
 
     v2VarBinds = []
 
@@ -114,21 +115,24 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
         # 3.1.2
         genericTrap = v1.apiTrapPDU.getGenericTrap(v1Pdu)
         if genericTrap == 6:
-            snmpTrapOIDParam = v1.apiTrapPDU.getEnterprise(v1Pdu) + (0, int(v1.apiTrapPDU.getSpecificTrap(v1Pdu)))
+            snmpTrapOIDParam = (v1.apiTrapPDU.getEnterprise(v1Pdu) +
+                                (0, int(v1.apiTrapPDU.getSpecificTrap(v1Pdu))))
 
         # 3.1.3
         else:
             snmpTrapOIDParam = v2c.ObjectIdentifier(V1_TO_V2_TRAP_MAP[genericTrap])
 
         # 3.1.4
-        v2VarBinds.append((v2c.apiTrapPDU.sysUpTime, sysUpTime))
-        v2VarBinds.append((v2c.apiTrapPDU.snmpTrapOID, snmpTrapOIDParam))
         v2VarBinds.append(
-            (v2c.apiTrapPDU.snmpTrapAddress, v1.apiTrapPDU.getAgentAddr(v1Pdu))
-        )
-        v2VarBinds.append((v2c.apiTrapPDU.snmpTrapCommunity, v2c.OctetString(snmpTrapCommunity)))
-        v2VarBinds.append((v2c.apiTrapPDU.snmpTrapEnterprise,
-                           v1.apiTrapPDU.getEnterprise(v1Pdu)))
+            (v2c.apiTrapPDU.sysUpTime, sysUpTime))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapOID, snmpTrapOIDParam))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapAddress, v1.apiTrapPDU.getAgentAddr(v1Pdu)))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapCommunity, v2c.OctetString(snmpTrapCommunity)))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapEnterprise, v1.apiTrapPDU.getEnterprise(v1Pdu)))
 
         varBinds = v1.apiTrapPDU.getVarBinds(v1Pdu)
 
@@ -142,13 +146,13 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
             v1Val = v1Val.getComponent()
 
         v2VarBinds.append(
-            (oid, V1_TO_V2_VALUE_MAP[v1Val.tagSet].clone(v1Val))
-        )
+            (oid, V1_TO_V2_VALUE_MAP[v1Val.tagSet].clone(v1Val)))
 
     if pduType in rfc3411.RESPONSE_CLASS_PDUS:
         # 4.1.2.2.1&2
         errorStatus = int(v1.apiPDU.getErrorStatus(v1Pdu))
         errorIndex = int(v1.apiPDU.getErrorIndex(v1Pdu, muteErrors=True))
+
         if errorStatus == 2:  # noSuchName
             if origV2Pdu.tagSet == v2c.GetNextRequestPDU.tagSet:
                 v2VarBinds = [(o, rfc1905.endOfMibView) for o, v in v2VarBinds]
@@ -171,13 +175,15 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
 
     v2c.apiPDU.setVarBinds(v2Pdu, v2VarBinds)
 
-    debug.logger & debug.FLAG_PRX and debug.logger('v1ToV2: v2Pdu %s' % v2Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v1ToV2: v2Pdu %s' % v2Pdu.prettyPrint())
 
     return v2Pdu
 
 
 def v2ToV1(v2Pdu, origV1Pdu=None):
-    debug.logger & debug.FLAG_PRX and debug.logger('v2ToV1: v2Pdu %s' % v2Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v2ToV1: v2Pdu %s' % v2Pdu.prettyPrint())
 
     pduType = v2Pdu.tagSet
 
@@ -224,7 +230,8 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
         for oid, val in v2VarBinds:
             # snmpTrapAddress
             if oid == v2c.apiTrapPDU.snmpTrapAddress:
-                v1.apiTrapPDU.setAgentAddr(v1Pdu, v1.IpAddress(val))  # v2c.OctetString is more constrained
+                # v2c.OctetString is more constrained
+                v1.apiTrapPDU.setAgentAddr(v1Pdu, v1.IpAddress(val))
                 break
 
         else:
@@ -232,7 +239,8 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
 
         # 3.2.3
         if snmpTrapOIDParam in V2_TO_V1_TRAP_MAP:
-            v1.apiTrapPDU.setGenericTrap(v1Pdu, V2_TO_V1_TRAP_MAP[snmpTrapOIDParam])
+            v1.apiTrapPDU.setGenericTrap(
+                v1Pdu, V2_TO_V1_TRAP_MAP[snmpTrapOIDParam])
 
         else:
             v1.apiTrapPDU.setGenericTrap(v1Pdu, 6)
@@ -273,6 +281,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
         while idx >= 0:
             # 4.1.2.1
             oid, val = v2VarBinds[idx]
+
             if v2c.Counter64.tagSet == val.tagSet:
                 if origV1Pdu.tagSet == v1.GetRequestPDU.tagSet:
                     v1.apiPDU.setErrorStatus(v1Pdu, 2)
@@ -298,8 +307,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
         v2ErrorStatus = v2c.apiPDU.getErrorStatus(v2Pdu)
         if v2ErrorStatus:
             v1.apiPDU.setErrorStatus(
-                v1Pdu, V2_TO_V1_ERROR_MAP.get(v2ErrorStatus, 5)
-            )
+                v1Pdu, V2_TO_V1_ERROR_MAP.get(v2ErrorStatus, 5))
             v1.apiPDU.setErrorIndex(v1Pdu, v2c.apiPDU.getErrorIndex(v2Pdu, muteErrors=True))
 
     elif pduType in rfc3411.CONFIRMED_CLASS_PDUS:
@@ -309,6 +317,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
     # Translate Var-Binds
     if (pduType in rfc3411.RESPONSE_CLASS_PDUS and
             v1.apiPDU.getErrorStatus(v1Pdu)):
+
         v1VarBinds = v1.apiPDU.getVarBinds(origV1Pdu)
 
     else:
@@ -327,6 +336,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
             v1Pdu, v2c.apiPDU.getRequestID(v2Pdu)
         )
 
-    debug.logger & debug.FLAG_PRX and debug.logger('v2ToV1: v1Pdu %s' % v1Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v2ToV1: v1Pdu %s' % v1Pdu.prettyPrint())
 
     return v1Pdu
diff --git a/pysnmp/proto/rfc1155.py b/pysnmp/proto/rfc1155.py
index e194f1c0..f78e6dc1 100644
--- a/pysnmp/proto/rfc1155.py
+++ b/pysnmp/proto/rfc1155.py
@@ -29,15 +29,19 @@ class IpAddress(univ.OctetString):
         if isinstance(value, str) and len(value) != 4:
             try:
                 value = [int(x) for x in value.split('.')]
-            except:
+
+            except Exception:
                 raise error.ProtocolError('Bad IP address syntax %s' % value)
+
         if len(value) != 4:
             raise error.ProtocolError('Bad IP address syntax')
+
         return univ.OctetString.prettyIn(self, value)
 
     def prettyOut(self, value):
         if value:
             return '.'.join(['%d' % x for x in self.__class__(value).asNumbers()])
+
         else:
             return ''
 
@@ -70,18 +74,24 @@ class NetworkAddress(univ.Choice):
             if the type of *value* is not allowed for this Choice instance.
         """
         cloned = univ.Choice.clone(self, **kwargs)
+
         if value is not univ.noValue:
             if isinstance(value, NetworkAddress):
                 value = value.getComponent()
+
             elif not isinstance(value, IpAddress):
                 # IpAddress is the only supported type, perhaps forever because
                 # this is SNMPv1.
                 value = IpAddress(value)
+
             try:
                 tagSet = value.tagSet
+
             except AttributeError:
                 raise PyAsn1Error('component value %r has no tag set' % (value,))
+
             cloned.setComponentByType(tagSet, value)
+
         return cloned
 
     # RFC 1212, section 4.1.6:
@@ -94,17 +104,21 @@ class NetworkAddress(univ.Choice):
     def cloneFromName(self, value, impliedFlag, parentRow, parentIndices):
         kind = value[0]
         clone = self.clone()
+
         if kind == 1:
             clone['internet'] = tuple(value[1:5])
             return clone, value[5:]
+
         else:
             raise SmiError('unknown NetworkAddress type %r' % (kind,))
 
     def cloneAsName(self, impliedFlag, parentRow, parentIndices):
         kind = self.getName()
         component = self.getComponent()
+
         if kind == 'internet':
             return (1,) + tuple(component.asNumbers())
+
         else:
             raise SmiError('unknown NetworkAddress type %r' % (kind,))
 
@@ -145,7 +159,9 @@ class TypeCoercionHackMixIn:  # XXX keep this old-style class till pyasn1 types
         if componentType:
             if idx >= len(componentType):
                 raise PyAsn1Error('Component type error out of range')
+
             t = componentType[idx].getType()
+
             if not t.getTagSet().isSuperTagSetOf(value.getTagSet()):
                 raise PyAsn1Error('Component type error %r vs %r' % (t, value))
 
diff --git a/pysnmp/proto/rfc1157.py b/pysnmp/proto/rfc1157.py
index b0ddbb08..30a26bc7 100644
--- a/pysnmp/proto/rfc1157.py
+++ b/pysnmp/proto/rfc1157.py
@@ -27,8 +27,9 @@ class VarBindList(univ.SequenceOf):
 
 
 errorStatus = univ.Integer(
-    namedValues=namedval.NamedValues(('noError', 0), ('tooBig', 1), ('noSuchName', 2),
-                                     ('badValue', 3), ('readOnly', 4), ('genErr', 5)))
+    namedValues=namedval.NamedValues(
+        ('noError', 0), ('tooBig', 1), ('noSuchName', 2),
+        ('badValue', 3), ('readOnly', 4), ('genErr', 5)))
 
 
 class _RequestBase(univ.Sequence):
@@ -65,8 +66,10 @@ class SetRequestPDU(_RequestBase):
 
 
 genericTrap = univ.Integer().clone(
-    namedValues=namedval.NamedValues(('coldStart', 0), ('warmStart', 1), ('linkDown', 2), ('linkUp', 3),
-                                     ('authenticationFailure', 4), ('egpNeighborLoss', 5), ('enterpriseSpecific', 6)))
+    namedValues=namedval.NamedValues(
+        ('coldStart', 0), ('warmStart', 1), ('linkDown', 2), ('linkUp', 3),
+        ('authenticationFailure', 4), ('egpNeighborLoss', 5),
+        ('enterpriseSpecific', 6)))
 
 
 class TrapPDU(univ.Sequence):
diff --git a/pysnmp/proto/rfc1902.py b/pysnmp/proto/rfc1902.py
index e1c037ee..50252c36 100644
--- a/pysnmp/proto/rfc1902.py
+++ b/pysnmp/proto/rfc1902.py
@@ -95,7 +95,8 @@ class Integer32(univ.Integer):
         """
 
         class X(cls):
-            subtypeSpec = cls.subtypeSpec + constraint.SingleValueConstraint(*values)
+            subtypeSpec = cls.subtypeSpec + constraint.SingleValueConstraint(
+                *values)
 
         X.__name__ = cls.__name__
         return X
@@ -106,7 +107,8 @@ class Integer32(univ.Integer):
         """
 
         class X(cls):
-            subtypeSpec = cls.subtypeSpec + constraint.ValueRangeConstraint(minimum, maximum)
+            subtypeSpec = cls.subtypeSpec + constraint.ValueRangeConstraint(
+                minimum, maximum)
 
         X.__name__ = cls.__name__
         return X
@@ -171,6 +173,7 @@ class Integer(Integer32):
                 *values.values())
 
         X.__name__ = cls.__name__
+
         return X
 
 
@@ -234,10 +237,12 @@ class OctetString(univ.OctetString):
         return self.fixedLength
 
     def clone(self, *args, **kwargs):
-        return univ.OctetString.clone(self, *args, **kwargs).setFixedLength(self.getFixedLength())
+        return univ.OctetString.clone(
+            self, *args, **kwargs).setFixedLength(self.getFixedLength())
 
     def subtype(self, *args, **kwargs):
-        return univ.OctetString.subtype(self, *args, **kwargs).setFixedLength(self.getFixedLength())
+        return univ.OctetString.subtype(
+            self, *args, **kwargs).setFixedLength(self.getFixedLength())
 
     @classmethod
     def withSize(cls, minimum, maximum):
@@ -245,7 +250,8 @@ class OctetString(univ.OctetString):
         """
 
         class X(cls):
-            subtypeSpec = cls.subtypeSpec + constraint.ValueSizeConstraint(minimum, maximum)
+            subtypeSpec = cls.subtypeSpec + constraint.ValueSizeConstraint(
+                minimum, maximum)
 
         X.__name__ = cls.__name__
         return X
@@ -328,11 +334,15 @@ class IpAddress(OctetString):
         if isinstance(value, str) and len(value) != 4:
             try:
                 value = [int(x) for x in value.split('.')]
-            except:
+
+            except Exception:
                 raise error.ProtocolError('Bad IP address syntax %s' % value)
+
         value = OctetString.prettyIn(self, value)
+
         if len(value) != 4:
             raise error.ProtocolError('Bad IP address syntax')
+
         return value
 
     def prettyOut(self, value):
@@ -340,6 +350,7 @@ class IpAddress(OctetString):
             return '.'.join(
                 ['%d' % x for x in self.__class__(value).asNumbers()]
             )
+
         else:
             return ''
 
@@ -643,30 +654,44 @@ class Bits(OctetString):
     def prettyIn(self, bits):
         if not isinstance(bits, (tuple, list)):
             return OctetString.prettyIn(self, bits)  # raw bitstring
+
         octets = []
+
         for bit in bits:  # tuple of named bits
             v = self.namedValues.getValue(bit)
+
             if v is None:
                 raise error.ProtocolError('Unknown named bit %s' % bit)
+
             d, m = divmod(v, 8)
             if d >= len(octets):
                 octets.extend([0] * (d - len(octets) + 1))
+
             octets[d] |= 0x01 << (7 - m)
+
         return OctetString.prettyIn(self, octets)
 
     def prettyOut(self, value):
         names = []
+
         ints = self.__class__(value).asNumbers()
+
         for i, v in enumerate(ints):
             v = ints[i]
+
             j = 7
+
             while j >= 0:
                 if v & (0x01 << j):
                     name = self.namedValues.getName(i * 8 + 7 - j)
+
                     if name is None:
                         name = 'UnknownBit-%s' % (i * 8 + 7 - j,)
+
                     names.append(name)
+
                 j -= 1
+
         return ', '.join([str(x) for x in names])
 
     @classmethod
diff --git a/pysnmp/proto/rfc1905.py b/pysnmp/proto/rfc1905.py
index 6a2637e2..15f56194 100644
--- a/pysnmp/proto/rfc1905.py
+++ b/pysnmp/proto/rfc1905.py
@@ -90,11 +90,12 @@ class VarBindList(univ.SequenceOf):
 
 errorStatus = univ.Integer(
     namedValues=namedval.NamedValues(
-        ('noError', 0), ('tooBig', 1), ('noSuchName', 2), ('badValue', 3), ('readOnly', 4),
-        ('genErr', 5), ('noAccess', 6), ('wrongType', 7), ('wrongLength', 8),
-        ('wrongEncoding', 9), ('wrongValue', 10), ('noCreation', 11),
-        ('inconsistentValue', 12), ('resourceUnavailable', 13), ('commitFailed', 14),
-        ('undoFailed', 15), ('authorizationError', 16), ('notWritable', 17),
+        ('noError', 0), ('tooBig', 1), ('noSuchName', 2), ('badValue', 3),
+        ('readOnly', 4), ('genErr', 5), ('noAccess', 6), ('wrongType', 7),
+        ('wrongLength', 8), ('wrongEncoding', 9), ('wrongValue', 10),
+        ('noCreation', 11), ('inconsistentValue', 12),
+        ('resourceUnavailable', 13), ('commitFailed', 14), ('undoFailed', 15),
+        ('authorizationError', 16), ('notWritable', 17),
         ('inconsistentName', 18))
     )
 
@@ -105,13 +106,17 @@ class PDU(univ.Sequence):
         namedtype.NamedType('request-id', rfc1902.Integer32()),
         namedtype.NamedType('error-status', errorStatus),
         namedtype.NamedType('error-index',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))),
+                            univ.Integer().subtype(
+                                subtypeSpec=constraint.ValueRangeConstraint(
+                                    0, max_bindings))),
         namedtype.NamedType('variable-bindings', VarBindList())
     )
 
 
-nonRepeaters = univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
-maxRepetitions = univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
+nonRepeaters = univ.Integer().subtype(
+    subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
+maxRepetitions = univ.Integer().subtype(
+    subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
 
 
 # Base class for bulk PDU
diff --git a/pysnmp/proto/rfc3412.py b/pysnmp/proto/rfc3412.py
index 7a3baa86..4e0f401c 100644
--- a/pysnmp/proto/rfc3412.py
+++ b/pysnmp/proto/rfc3412.py
@@ -28,6 +28,7 @@ class MsgAndPduDispatcher(object):
             self.mibInstrumController = instrum.MibInstrumController(
                 builder.MibBuilder()
             )
+
         else:
             self.mibInstrumController = mibInstrumController
 
@@ -37,25 +38,25 @@ class MsgAndPduDispatcher(object):
         )
 
         # Requests cache
-        self.__cache = cache.Cache()
+        self._cache = cache.Cache()
 
         # Registered context engine IDs
-        self.__appsRegistration = {}
+        self._appsRegistration = {}
 
         # Source of sendPduHandle and cache of requesting apps
-        self.__sendPduHandle = nextid.Integer(0xffffff)
+        self._sendPduHandle = nextid.Integer(0xffffff)
 
         # To pass transport info to app (legacy)
-        self.__transportInfo = {}
+        self._transportInfo = {}
 
     # legacy
     def getTransportInfo(self, stateReference):
-        if stateReference in self.__transportInfo:
-            return self.__transportInfo[stateReference]
+        if stateReference in self._transportInfo:
+            return self._transportInfo[stateReference]
+
         else:
             raise error.ProtocolError(
-                'No data for stateReference %s' % stateReference
-            )
+                'No data for stateReference %s' % stateReference)
 
     # Application registration with dispatcher
 
@@ -66,42 +67,45 @@ class MsgAndPduDispatcher(object):
 
         # 4.3.3
         for pduType in pduTypes:
-            k = (contextEngineId, pduType)
-            if k in self.__appsRegistration:
+            k = contextEngineId, pduType
+            if k in self._appsRegistration:
                 raise error.ProtocolError(
-                    'Duplicate registration %r/%s' % (contextEngineId, pduType)
-                )
+                    'Duplicate registration %r/%s' % (contextEngineId, pduType))
 
             # 4.3.4
-            self.__appsRegistration[k] = processPdu
+            self._appsRegistration[k] = processPdu
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'registerContextEngineId: contextEngineId %r pduTypes %s' % (contextEngineId, pduTypes))
+            'registerContextEngineId: contextEngineId %r pduTypes '
+            '%s' % (contextEngineId, pduTypes))
 
     # 4.4.1
     def unregisterContextEngineId(self, contextEngineId, pduTypes):
         """Unregister application with dispatcher"""
+
         # 4.3.4
         if contextEngineId is None:
             # Default to local snmpEngineId
-            contextEngineId, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                  'snmpEngineID')
+            contextEngineId, = self.mibInstrumController.mibBuilder.importSymbols(
+                '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
         for pduType in pduTypes:
-            k = (contextEngineId, pduType)
-            if k in self.__appsRegistration:
-                del self.__appsRegistration[k]
+            k = contextEngineId, pduType
+            if k in self._appsRegistration:
+                del self._appsRegistration[k]
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'unregisterContextEngineId: contextEngineId %r pduTypes %s' % (contextEngineId, pduTypes))
+            'unregisterContextEngineId: contextEngineId %r pduTypes '
+            '%s' % (contextEngineId, pduTypes))
 
     def getRegisteredApp(self, contextEngineId, pduType):
-        k = (contextEngineId, pduType)
-        if k in self.__appsRegistration:
-            return self.__appsRegistration[k]
-        k = (null, pduType)
-        if k in self.__appsRegistration:
-            return self.__appsRegistration[k]  # wildcard
+        k = contextEngineId, pduType
+        if k in self._appsRegistration:
+            return self._appsRegistration[k]
+
+        k = null, pduType
+        if k in self._appsRegistration:
+            return self._appsRegistration[k]  # wildcard
 
     # Dispatcher <-> application API
 
@@ -115,20 +119,23 @@ class MsgAndPduDispatcher(object):
         """PDU dispatcher -- prepare and serialize a request or notification"""
         # 4.1.1.2
         k = int(messageProcessingModel)
+
         if k in snmpEngine.messageProcessingSubsystems:
             mpHandler = snmpEngine.messageProcessingSubsystems[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedMsgProcessingModel
-            )
+                errorIndication=errind.unsupportedMsgProcessingModel)
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'sendPdu: securityName %s, PDU\n%s' % (securityName, PDU.prettyPrint()))
+            'sendPdu: securityName %s, PDU\n'
+            '%s' % (securityName, PDU.prettyPrint()))
 
         # 4.1.1.3
-        sendPduHandle = self.__sendPduHandle()
+        sendPduHandle = self._sendPduHandle()
+
         if expectResponse:
-            self.__cache.add(
+            self._cache.add(
                 sendPduHandle,
                 messageProcessingModel=messageProcessingModel,
                 sendPduHandle=sendPduHandle,
@@ -137,11 +144,14 @@ class MsgAndPduDispatcher(object):
                 cbCtx=cbCtx
             )
 
-            debug.logger & debug.FLAG_DSP and debug.logger('sendPdu: current time %d ticks, one tick is %s seconds' % (
-                snmpEngine.transportDispatcher.getTimerTicks(), snmpEngine.transportDispatcher.getTimerResolution()))
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'sendPdu: current time %d ticks, one tick is %s '
+                'seconds' % (snmpEngine.transportDispatcher.getTimerTicks(),
+                             snmpEngine.transportDispatcher.getTimerResolution()))
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'sendPdu: new sendPduHandle %s, timeout %s ticks, cbFun %s' % (sendPduHandle, timeout, cbFun))
+            'sendPdu: new sendPduHandle %s, timeout %s ticks, cbFun '
+            '%s' % (sendPduHandle, timeout, cbFun))
 
         origTransportDomain = transportDomain
         origTransportAddress = transportAddress
@@ -157,17 +167,20 @@ class MsgAndPduDispatcher(object):
                 pduVersion, PDU, expectResponse, sendPduHandle
             )
 
-            debug.logger & debug.FLAG_DSP and debug.logger('sendPdu: MP succeeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'sendPdu: MP succeeded')
+
         except PySnmpError:
             if expectResponse:
-                self.__cache.pop(sendPduHandle)
+                self._cache.pop(sendPduHandle)
                 self.releaseStateInformation(snmpEngine, sendPduHandle, messageProcessingModel)
+
             raise
 
         # 4.1.1.6
         if snmpEngine.transportDispatcher is None:
             if expectResponse:
-                self.__cache.pop(sendPduHandle)
+                self._cache.pop(sendPduHandle)
 
             raise error.PySnmpError('Transport dispatcher not set')
 
@@ -187,27 +200,30 @@ class MsgAndPduDispatcher(object):
 
         try:
             snmpEngine.transportDispatcher.sendMessage(
-                outgoingMessage, transportDomain, transportAddress
-            )
+                outgoingMessage, transportDomain, transportAddress)
+
         except PySnmpError:
             if expectResponse:
-                self.__cache.pop(sendPduHandle)
+                self._cache.pop(sendPduHandle)
             raise
 
-        snmpEngine.observer.clearExecutionContext(snmpEngine, 'rfc3412.sendPdu')
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc3412.sendPdu')
 
         # Update cache with orignal req params (used for retrying)
         if expectResponse:
-            self.__cache.update(sendPduHandle,
-                                transportDomain=origTransportDomain,
-                                transportAddress=origTransportAddress,
-                                securityModel=securityModel,
-                                securityName=securityName,
-                                securityLevel=securityLevel,
-                                contextEngineId=contextEngineId,
-                                contextName=contextName,
-                                pduVersion=pduVersion,
-                                PDU=PDU)
+            self._cache.update(
+                sendPduHandle,
+                transportDomain=origTransportDomain,
+                transportAddress=origTransportAddress,
+                securityModel=securityModel,
+                securityName=securityName,
+                securityLevel=securityLevel,
+                contextEngineId=contextEngineId,
+                contextName=contextName,
+                pduVersion=pduVersion,
+                PDU=PDU
+            )
 
         return sendPduHandle
 
@@ -217,17 +233,20 @@ class MsgAndPduDispatcher(object):
                           contextEngineId, contextName, pduVersion,
                           PDU, maxSizeResponseScopedPDU, stateReference,
                           statusInformation):
+
         # Extract input values and initialize defaults
         k = int(messageProcessingModel)
+
         if k in snmpEngine.messageProcessingSubsystems:
             mpHandler = snmpEngine.messageProcessingSubsystems[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedMsgProcessingModel
-            )
+                errorIndication=errind.unsupportedMsgProcessingModel)
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'returnResponsePdu: PDU %s' % (PDU and PDU.prettyPrint() or "<empty>",))
+            'returnResponsePdu: PDU '
+            '%s' % (PDU and PDU.prettyPrint() or "<empty>",))
 
         # 4.1.2.2
         try:
@@ -240,19 +259,26 @@ class MsgAndPduDispatcher(object):
                 statusInformation
             )
 
-            debug.logger & debug.FLAG_DSP and debug.logger('returnResponsePdu: MP suceeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'returnResponsePdu: MP suceeded')
 
         except error.StatusInformation:
             # 4.1.2.3
             raise
 
+        mibBuilder = self.mibInstrumController.mibBuilder
+
         # Handle oversized messages XXX transport constrains?
-        snmpEngineMaxMessageSize, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                       'snmpEngineMaxMessageSize')
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
+
         if (snmpEngineMaxMessageSize.syntax and
                 len(outgoingMessage) > snmpEngineMaxMessageSize.syntax):
-            snmpSilentDrops, = self.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpSilentDrops')
+
+            snmpSilentDrops, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpSilentDrops')
             snmpSilentDrops.syntax += 1
+
             raise error.StatusInformation(errorIndication=errind.tooBig)
 
         snmpEngine.observer.storeExecutionContext(
@@ -271,45 +297,50 @@ class MsgAndPduDispatcher(object):
         )
 
         # 4.1.2.4
-        snmpEngine.transportDispatcher.sendMessage(outgoingMessage,
-                                                   transportDomain,
-                                                   transportAddress)
+        snmpEngine.transportDispatcher.sendMessage(
+            outgoingMessage, transportDomain, transportAddress)
 
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc3412.returnResponsePdu'
-        )
+            snmpEngine, 'rfc3412.returnResponsePdu')
 
     # 4.2.1
     def receiveMessage(self, snmpEngine, transportDomain,
                        transportAddress, wholeMsg):
         """Message dispatcher -- de-serialize message into PDU"""
+        mibBuilder = self.mibInstrumController.mibBuilder
+
         # 4.2.1.1
-        snmpInPkts, = self.mibInstrumController.mibBuilder.importSymbols(
-            '__SNMPv2-MIB', 'snmpInPkts'
-        )
+        snmpInPkts, = mibBuilder.importSymbols(
+            '__SNMPv2-MIB', 'snmpInPkts')
         snmpInPkts.syntax += 1
 
+        restOfWholeMsg = null  # XXX fix decoder non-recursive return
+
         # 4.2.1.2
         try:
-            restOfWholeMsg = null  # XXX fix decoder non-recursive return
             msgVersion = verdec.decodeMessageVersion(wholeMsg)
 
         except error.ProtocolError:
-            snmpInASNParseErrs, = self.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB',
-                                                                                     'snmpInASNParseErrs')
+            snmpInASNParseErrs, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpInASNParseErrs')
             snmpInASNParseErrs.syntax += 1
+
             return null  # n.b the whole buffer gets dropped
 
-        debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: msgVersion %s, msg decoded' % msgVersion)
+        debug.logger & debug.FLAG_DSP and debug.logger(
+            'receiveMessage: msgVersion %s, msg decoded' % msgVersion)
 
         messageProcessingModel = msgVersion
 
         try:
-            mpHandler = snmpEngine.messageProcessingSubsystems[int(messageProcessingModel)]
+            mpHandler = snmpEngine.messageProcessingSubsystems[
+                int(messageProcessingModel)]
 
         except KeyError:
-            snmpInBadVersions, = self.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInBadVersions')
+            snmpInBadVersions, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpInBadVersions')
             snmpInBadVersions.syntax += 1
+
             return restOfWholeMsg
 
         # 4.2.1.3 -- no-op
@@ -329,48 +360,56 @@ class MsgAndPduDispatcher(object):
              maxSizeResponseScopedPDU,
              statusInformation,
              stateReference) = mpHandler.prepareDataElements(
-                snmpEngine, transportDomain, transportAddress, wholeMsg
-            )
+                snmpEngine, transportDomain, transportAddress, wholeMsg)
 
-            debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: MP succeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'receiveMessage: MP succeded')
 
         except error.StatusInformation as exc:
             statusInformation = exc
+
             if 'sendPduHandle' in statusInformation:
                 # Dropped REPORT -- re-run pending reqs queue as some
                 # of them may be waiting for this REPORT
                 debug.logger & debug.FLAG_DSP and debug.logger(
-                    'receiveMessage: MP failed, statusInformation %s, forcing a retry' % statusInformation)
+                    'receiveMessage: MP failed, statusInformation %s, '
+                    'forcing retry' % statusInformation)
+
                 self.__expireRequest(
                     statusInformation['sendPduHandle'],
-                    self.__cache.pop(statusInformation['sendPduHandle']),
+                    self._cache.pop(statusInformation['sendPduHandle']),
                     snmpEngine,
-                    statusInformation
-                )
+                    statusInformation)
+
             return restOfWholeMsg
 
         except PyAsn1Error as exc:
-            debug.logger & debug.FLAG_MP and debug.logger('receiveMessage: %s' % exc)
-            snmpInASNParseErrs, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInASNParseErrs')
+            debug.logger & debug.FLAG_MP and debug.logger(
+                'receiveMessage: %s' % exc)
+            snmpInASNParseErrs, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpInASNParseErrs')
             snmpInASNParseErrs.syntax += 1
 
             return restOfWholeMsg
 
-        debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: PDU %s' % PDU.prettyPrint())
+        debug.logger & debug.FLAG_DSP and debug.logger(
+            'receiveMessage: PDU %s' % PDU.prettyPrint())
 
         # 4.2.2
         if sendPduHandle is None:
             # 4.2.2.1 (request or notification)
 
-            debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: pduType %s' % pduType)
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'receiveMessage: pduType %s' % pduType)
+
             # 4.2.2.1.1
             processPdu = self.getRegisteredApp(contextEngineId, pduType)
 
             # 4.2.2.1.2
             if processPdu is None:
                 # 4.2.2.1.2.a
-                snmpUnknownPDUHandlers, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-MPD-MIB',
-                                                                                             'snmpUnknownPDUHandlers')
+                snmpUnknownPDUHandlers, = importSymbols(
+                    '__SNMP-MPD-MIB', 'snmpUnknownPDUHandlers')
                 snmpUnknownPDUHandlers.syntax += 1
 
                 # 4.2.2.1.2.b
@@ -380,7 +419,8 @@ class MsgAndPduDispatcher(object):
                     'val': snmpUnknownPDUHandlers.syntax
                 }
 
-                debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: unhandled PDU type')
+                debug.logger & debug.FLAG_DSP and debug.logger(
+                    'receiveMessage: unhandled PDU type')
 
                 # 4.2.2.1.2.c
                 try:
@@ -391,20 +431,19 @@ class MsgAndPduDispatcher(object):
                         securityModel, securityName, securityLevel,
                         contextEngineId, contextName, pduVersion,
                         PDU, maxSizeResponseScopedPDU, stateReference,
-                        statusInformation
-                    )
+                        statusInformation)
 
                     snmpEngine.transportDispatcher.sendMessage(
                         outgoingMessage, destTransportDomain,
-                        destTransportAddress
-                    )
+                        destTransportAddress)
 
                 except PySnmpError as exc:
                     debug.logger & debug.FLAG_DSP and debug.logger(
                         'receiveMessage: report failed, statusInformation %s' % exc)
 
                 else:
-                    debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: reporting succeeded')
+                    debug.logger & debug.FLAG_DSP and debug.logger(
+                        'receiveMessage: reporting succeeded')
 
                 # 4.2.2.1.2.d
                 return restOfWholeMsg
@@ -421,42 +460,44 @@ class MsgAndPduDispatcher(object):
                          securityLevel=securityLevel,
                          contextEngineId=contextEngineId,
                          contextName=contextName,
-                         pdu=PDU)
-                )
+                         pdu=PDU))
 
                 # pass transport info to app (legacy)
                 if stateReference is not None:
-                    self.__transportInfo[stateReference] = (
-                        transportDomain, transportAddress
-                    )
+                    self._transportInfo[stateReference] = (
+                        transportDomain, transportAddress)
 
                 # 4.2.2.1.3 (asynchronous function)
-                processPdu(snmpEngine, messageProcessingModel,
-                           securityModel, securityName, securityLevel,
-                           contextEngineId, contextName, pduVersion,
-                           PDU, maxSizeResponseScopedPDU, stateReference)
+                processPdu(
+                    snmpEngine, messageProcessingModel, securityModel,
+                    securityName, securityLevel, contextEngineId,
+                    contextName, pduVersion, PDU, maxSizeResponseScopedPDU,
+                    stateReference)
 
                 snmpEngine.observer.clearExecutionContext(
-                    snmpEngine, 'rfc3412.receiveMessage:request'
-                )
+                    snmpEngine, 'rfc3412.receiveMessage:request')
 
                 # legacy
                 if stateReference is not None:
-                    del self.__transportInfo[stateReference]
+                    del self._transportInfo[stateReference]
+
+                debug.logger & debug.FLAG_DSP and debug.logger(
+                    'receiveMessage: processPdu initiated')
 
-                debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: processPdu initiated')
                 return restOfWholeMsg
+
         else:
             # 4.2.2.2 (response)
 
             # 4.2.2.2.1
-            cachedParams = self.__cache.pop(sendPduHandle)
+            cachedParams = self._cache.pop(sendPduHandle)
 
             # 4.2.2.2.2
             if cachedParams is None:
-                snmpUnknownPDUHandlers, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-MPD-MIB',
-                                                                                             'snmpUnknownPDUHandlers')
+                snmpUnknownPDUHandlers, = mibBuilder.importSymbols(
+                    '__SNMP-MPD-MIB', 'snmpUnknownPDUHandlers')
                 snmpUnknownPDUHandlers.syntax += 1
+
                 return restOfWholeMsg
 
             debug.logger & debug.FLAG_DSP and debug.logger(
@@ -476,42 +517,44 @@ class MsgAndPduDispatcher(object):
                      securityLevel=securityLevel,
                      contextEngineId=contextEngineId,
                      contextName=contextName,
-                     pdu=PDU)
-            )
+                     pdu=PDU))
 
             # 4.2.2.2.4
             processResponsePdu = cachedParams['cbFun']
 
-            processResponsePdu(snmpEngine, messageProcessingModel,
-                               securityModel, securityName, securityLevel,
-                               contextEngineId, contextName, pduVersion,
-                               PDU, statusInformation,
-                               cachedParams['sendPduHandle'],
-                               cachedParams['cbCtx'])
+            processResponsePdu(
+                snmpEngine, messageProcessingModel, securityModel,
+                securityName, securityLevel, contextEngineId, contextName,
+                pduVersion, PDU, statusInformation,
+                cachedParams['sendPduHandle'],
+                cachedParams['cbCtx'])
 
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.receiveMessage:response'
-            )
+                snmpEngine, 'rfc3412.receiveMessage:response')
 
-            debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: processResponsePdu succeeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'receiveMessage: processResponsePdu succeeded')
 
             return restOfWholeMsg
 
     def releaseStateInformation(self, snmpEngine, sendPduHandle,
                                 messageProcessingModel):
         k = int(messageProcessingModel)
+
         if k in snmpEngine.messageProcessingSubsystems:
             mpHandler = snmpEngine.messageProcessingSubsystems[k]
             mpHandler.releaseStateInformation(sendPduHandle)
 
-        self.__cache.pop(sendPduHandle)
+        self._cache.pop(sendPduHandle)
 
     # Cache expiration stuff
 
     # noinspection PyUnusedLocal
     def __expireRequest(self, cacheKey, cachedParams, snmpEngine,
                         statusInformation=None):
+
         timeNow = snmpEngine.transportDispatcher.getTimerTicks()
+
         timeoutAt = cachedParams['timeout']
 
         if statusInformation is None and timeNow < timeoutAt:
@@ -519,24 +562,25 @@ class MsgAndPduDispatcher(object):
 
         processResponsePdu = cachedParams['cbFun']
 
-        debug.logger & debug.FLAG_DSP and debug.logger('__expireRequest: req cachedParams %s' % cachedParams)
+        debug.logger & debug.FLAG_DSP and debug.logger(
+            '__expireRequest: req cachedParams %s' % cachedParams)
 
         # Fail timed-out requests
         if not statusInformation:
             statusInformation = error.StatusInformation(
-                errorIndication=errind.requestTimedOut
-            )
+                errorIndication=errind.requestTimedOut)
+
+        self.releaseStateInformation(
+            snmpEngine, cachedParams['sendPduHandle'],
+            cachedParams['messageProcessingModel'])
 
-        self.releaseStateInformation(snmpEngine,
-                                     cachedParams['sendPduHandle'],
-                                     cachedParams['messageProcessingModel'])
+        processResponsePdu(
+            snmpEngine, None, None, None, None, None, None, None, None,
+            statusInformation,
+            cachedParams['sendPduHandle'], cachedParams['cbCtx'])
 
-        processResponsePdu(snmpEngine, None, None, None, None, None,
-                           None, None, None, statusInformation,
-                           cachedParams['sendPduHandle'],
-                           cachedParams['cbCtx'])
         return True
 
     # noinspection PyUnusedLocal
     def receiveTimerTick(self, snmpEngine, timeNow):
-        self.__cache.expire(self.__expireRequest, snmpEngine)
+        self._cache.expire(self.__expireRequest, snmpEngine)
diff --git a/pysnmp/proto/secmod/cache.py b/pysnmp/proto/secmod/cache.py
index f5843c50..1859bbad 100644
--- a/pysnmp/proto/secmod/cache.py
+++ b/pysnmp/proto/secmod/cache.py
@@ -21,10 +21,8 @@ class Cache(object):
 
     def pop(self, stateReference):
         if stateReference in self.__cacheEntries:
-            securityData = self.__cacheEntries[stateReference]
-        else:
-            raise error.ProtocolError(
-                'Cache miss for stateReference=%s at %s' % (stateReference, self)
-            )
-        del self.__cacheEntries[stateReference]
-        return securityData
+            return self.__cacheEntries.pop(stateReference)
+
+        raise error.ProtocolError(
+            'Cache miss for stateReference=%s at '
+            '%s' % (stateReference, self))
diff --git a/pysnmp/proto/secmod/eso/priv/aes192.py b/pysnmp/proto/secmod/eso/priv/aes192.py
index 7df0a0f5..cbbc748e 100644
--- a/pysnmp/proto/secmod/eso/priv/aes192.py
+++ b/pysnmp/proto/secmod/eso/priv/aes192.py
@@ -14,7 +14,8 @@ class AesBlumenthal192(aesbase.AbstractAesBlumenthal):
 
        http://tools.ietf.org/html/draft-blumenthal-aes-usm-04
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 1)  # cusmAESCfb192PrivProtocol
+    # cusmAESCfb192PrivProtocol
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 1)
     KEY_SIZE = 24
 
 
@@ -29,5 +30,6 @@ class Aes192(aesbase.AbstractAesReeder):
 
     Known to be used by many vendors including Cisco and others.
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 101)  # cusmAESCfb192PrivProtocol (non-standard OID)
+    # cusmAESCfb192PrivProtocol (non-standard OID)
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 101)
     KEY_SIZE = 24
diff --git a/pysnmp/proto/secmod/eso/priv/aes256.py b/pysnmp/proto/secmod/eso/priv/aes256.py
index 94a255ff..7ca42504 100644
--- a/pysnmp/proto/secmod/eso/priv/aes256.py
+++ b/pysnmp/proto/secmod/eso/priv/aes256.py
@@ -12,7 +12,8 @@ class AesBlumenthal256(aesbase.AbstractAesBlumenthal):
 
        http://tools.ietf.org/html/draft-blumenthal-aes-usm-04
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 2)  # cusmAESCfb256PrivProtocol
+    # cusmAESCfb256PrivProtocol
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 2)
     KEY_SIZE = 32
 
 
@@ -27,5 +28,6 @@ class Aes256(aesbase.AbstractAesReeder):
 
     Known to be used by many vendors including Cisco and others.
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 102)  # cusmAESCfb256PrivProtocol (non-standard OID)
+    # cusmAESCfb256PrivProtocol (non-standard OID)
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 102)
     KEY_SIZE = 32
diff --git a/pysnmp/proto/secmod/eso/priv/aesbase.py b/pysnmp/proto/secmod/eso/priv/aesbase.py
index 0c2e5d17..3af30df0 100644
--- a/pysnmp/proto/secmod/eso/priv/aesbase.py
+++ b/pysnmp/proto/secmod/eso/priv/aesbase.py
@@ -24,19 +24,25 @@ class AbstractAesBlumenthal(aes.Aes):
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
 
-        localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
+        localPrivKey = localkey.localizeKey(
+            privKey, snmpEngineID, hashAlgo)
 
-        # now extend this key if too short by repeating steps that includes the hashPassphrase step
-        for count in range(1, int(ceil(self.KEY_SIZE * 1.0 / len(localPrivKey)))):
+        # now extend this key if too short by repeating steps that includes
+        # the hashPassphrase step
+        rounds = int(ceil(self.KEY_SIZE * 1.0 / len(localPrivKey)))
+
+        for _ in range(1, rounds):
             localPrivKey += hashAlgo(localPrivKey).digest()
 
         return localPrivKey[:self.KEY_SIZE]
@@ -64,14 +70,16 @@ class AbstractAesReeder(aes.Aes):
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
 
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
 
diff --git a/pysnmp/proto/secmod/eso/priv/des3.py b/pysnmp/proto/secmod/eso/priv/des3.py
index da84475b..8d193084 100644
--- a/pysnmp/proto/secmod/eso/priv/des3.py
+++ b/pysnmp/proto/secmod/eso/priv/des3.py
@@ -34,7 +34,8 @@ class Des3(base.AbstractEncryptionService):
 
        https://tools.ietf.org/html/draft-reeder-snmpv3-usm-3desede-00
     """
-    SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3)  # usm3DESEDEPrivProtocol
+    # usm3DESEDEPrivProtocol
+    SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3)
     KEY_SIZE = 32
 
     local_int = random.randrange(0, 0xffffffff)
@@ -42,28 +43,34 @@ class Des3(base.AbstractEncryptionService):
     def hashPassphrase(self, authProtocol, privKey):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         return localkey.hashPassphrase(privKey, hashAlgo)
 
     # 2.1
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
 
         # now extend this key if too short by repeating steps that includes the hashPassphrase step
@@ -75,7 +82,7 @@ class Des3(base.AbstractEncryptionService):
         return localPrivKey[:self.KEY_SIZE]
 
     # 5.1.1.1
-    def __getEncryptionKey(self, privKey, snmpEngineBoots):
+    def _getEncryptionKey(self, privKey, snmpEngineBoots):
         # 5.1.1.1.1
         des3Key = privKey[:24]
         preIV = privKey[24:32]
@@ -94,39 +101,46 @@ class Des3(base.AbstractEncryptionService):
         ]
         if self.local_int == 0xffffffff:
             self.local_int = 0
+
         else:
             self.local_int += 1
 
         # salt not yet hashed XXX
 
+        iv = map(lambda x, y: x ^ y, salt, preIV.asNumbers())
+
         return (des3Key.asOctets(),
                 univ.OctetString(salt).asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt, preIV.asNumbers())).asOctets())
+                univ.OctetString(iv).asOctets())
 
     @staticmethod
-    def __getDecryptionKey(privKey, salt):
+    def _getDecryptionKey(privKey, salt):
+        iv = map(
+            lambda x, y: x ^ y, salt.asNumbers(), privKey[24:32].asNumbers())
+
         return (privKey[:24].asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt.asNumbers(), privKey[24:32].asNumbers())).asOctets())
+                univ.OctetString(iv).asOctets())
 
     # 5.1.1.2
     def encryptData(self, encryptKey, privParameters, dataToEncrypt):
         snmpEngineBoots, snmpEngineTime, salt = privParameters
 
-        des3Key, salt, iv = self.__getEncryptionKey(
+        des3Key, salt, iv = self._getEncryptionKey(
             encryptKey, snmpEngineBoots
         )
 
         privParameters = univ.OctetString(salt)
 
-        plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
+        plaintext = dataToEncrypt
+        plaintext += univ.OctetString(
+            (0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
 
         try:
             ciphertext = des3.encrypt(plaintext, des3Key, iv)
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         return univ.OctetString(ciphertext), privParameters
 
@@ -136,15 +150,13 @@ class Des3(base.AbstractEncryptionService):
 
         if len(salt) != 8:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
-        des3Key, iv = self.__getDecryptionKey(decryptKey, salt)
+        des3Key, iv = self._getDecryptionKey(decryptKey, salt)
 
         if len(encryptedData) % 8 != 0:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         ciphertext = encryptedData.asOctets()
 
@@ -153,7 +165,6 @@ class Des3(base.AbstractEncryptionService):
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         return plaintext
diff --git a/pysnmp/proto/secmod/rfc2576.py b/pysnmp/proto/secmod/rfc2576.py
index ba11b0fe..92b5eac2 100644
--- a/pysnmp/proto/secmod/rfc2576.py
+++ b/pysnmp/proto/secmod/rfc2576.py
@@ -4,9 +4,6 @@
 # Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
 # License: http://snmplabs.com/pysnmp/license.html
 #
-from pyasn1.codec.ber import encoder
-from pyasn1.error import PyAsn1Error
-
 from pysnmp import debug
 from pysnmp.carrier.asyncore.dgram import udp
 from pysnmp.carrier.asyncore.dgram import udp6
@@ -15,6 +12,9 @@ from pysnmp.proto import error
 from pysnmp.proto.secmod import base
 from pysnmp.smi.error import NoSuchInstanceError
 
+from pyasn1.codec.ber import encoder
+from pyasn1.error import PyAsn1Error
+
 
 class SnmpV1SecurityModel(base.AbstractSecurityModel):
     SECURITY_MODEL_ID = 1
@@ -26,60 +26,69 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
     # in here.
 
     def __init__(self):
-        self.__transportBranchId = self.__paramsBranchId = self.__communityBranchId = self.__securityBranchId = -1
+        self._transportBranchId = -1
+        self._paramsBranchId = -1
+        self._communityBranchId = -1
+        self._securityBranchId = -1
+
         base.AbstractSecurityModel.__init__(self)
 
     def _sec2com(self, snmpEngine, securityName, contextEngineId, contextName):
-        snmpTargetParamsSecurityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpTargetParamsSecurityName, = mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityName')
-        if self.__paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
-            snmpTargetParamsSecurityModel, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+
+        if self._paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
+            snmpTargetParamsSecurityModel, = mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityModel')
 
-            self.__nameToModelMap = {}
+            self._nameToModelMap = {}
 
             nextMibNode = snmpTargetParamsSecurityName
 
             while True:
                 try:
-                    nextMibNode = snmpTargetParamsSecurityName.getNextNode(nextMibNode.name)
+                    nextMibNode = snmpTargetParamsSecurityName.getNextNode(
+                        nextMibNode.name)
 
                 except NoSuchInstanceError:
                     break
 
                 instId = nextMibNode.name[len(snmpTargetParamsSecurityName.name):]
 
-                mibNode = snmpTargetParamsSecurityModel.getNode(snmpTargetParamsSecurityModel.name + instId)
+                mibNode = snmpTargetParamsSecurityModel.getNode(
+                    snmpTargetParamsSecurityModel.name + instId)
 
                 try:
-                    if mibNode.syntax not in self.__nameToModelMap:
-                        self.__nameToModelMap[nextMibNode.syntax] = set()
+                    if mibNode.syntax not in self._nameToModelMap:
+                        self._nameToModelMap[nextMibNode.syntax] = set()
 
-                    self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
+                    self._nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_sec2com: table entries %r/%r hashing failed' % (
-                            nextMibNode.syntax, mibNode.syntax)
-                    )
+                        '_sec2com: table entries %r/%r hashing '
+                        'failed' % (nextMibNode.syntax, mibNode.syntax))
                     continue
 
-            self.__paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
+            self._paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
 
             # invalidate next map as it include this one
-            self.__securityBranchId = -1
+            self._securityBranchId = -1
 
-        snmpCommunityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMP-COMMUNITY-MIB',
-                                                                                                   'snmpCommunityName')
-        if self.__securityBranchId != snmpCommunityName.branchVersionId:
+        snmpCommunityName, = mibBuilder.importSymbols(
+            'SNMP-COMMUNITY-MIB', 'snmpCommunityName')
+
+        if self._securityBranchId != snmpCommunityName.branchVersionId:
             (snmpCommunitySecurityName,
              snmpCommunityContextEngineId,
-             snmpCommunityContextName) = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+             snmpCommunityContextName) = mibBuilder.importSymbols(
                 'SNMP-COMMUNITY-MIB', 'snmpCommunitySecurityName',
                 'snmpCommunityContextEngineID', 'snmpCommunityContextName'
             )
 
-            self.__securityMap = {}
+            self._securityMap = {}
 
             nextMibNode = snmpCommunityName
 
@@ -92,54 +101,55 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 instId = nextMibNode.name[len(snmpCommunityName.name):]
 
-                _securityName = snmpCommunitySecurityName.getNode(snmpCommunitySecurityName.name + instId).syntax
+                _securityName = snmpCommunitySecurityName.getNode(
+                    snmpCommunitySecurityName.name + instId).syntax
 
                 _contextEngineId = snmpCommunityContextEngineId.getNode(
                     snmpCommunityContextEngineId.name + instId).syntax
 
-                _contextName = snmpCommunityContextName.getNode(snmpCommunityContextName.name + instId).syntax
+                _contextName = snmpCommunityContextName.getNode(
+                    snmpCommunityContextName.name + instId).syntax
+
+                key = _securityName, _contextEngineId, _contextName
 
                 try:
-                    self.__securityMap[(_securityName,
-                                        _contextEngineId,
-                                        _contextName)] = nextMibNode.syntax
+                    self._securityMap[key] = nextMibNode.syntax
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_sec2com: table entries %r/%r/%r hashing failed' % (
-                            _securityName, _contextEngineId, _contextName)
-                    )
+                        '_sec2com: table entries %r/%r/%r hashing failed' % key)
                     continue
 
-            self.__securityBranchId = snmpCommunityName.branchVersionId
+            self._securityBranchId = snmpCommunityName.branchVersionId
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_sec2com: built securityName to communityName map, version %s: %s' % (
-                    self.__securityBranchId, self.__securityMap))
+                '_sec2com: built securityName to communityName map, version '
+                '%s: %s' % (self._securityBranchId, self._securityMap))
+
+        key = securityName, contextEngineId, contextName
 
         try:
-            return self.__securityMap[(securityName,
-                                       contextEngineId,
-                                       contextName)]
+            return self._securityMap[key]
 
         except KeyError:
             raise error.StatusInformation(
-                errorIndication=errind.unknownCommunityName
-            )
+                errorIndication=errind.unknownCommunityName)
 
     def _com2sec(self, snmpEngine, communityName, transportInformation):
-        snmpTargetAddrTAddress, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpTargetAddrTAddress, = mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetAddrTAddress')
-        if self.__transportBranchId != snmpTargetAddrTAddress.branchVersionId:
+
+        if self._transportBranchId != snmpTargetAddrTAddress.branchVersionId:
             (SnmpTagValue, snmpTargetAddrTDomain,
-             snmpTargetAddrTagList) = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+             snmpTargetAddrTagList) = mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'SnmpTagValue', 'snmpTargetAddrTDomain',
-                'snmpTargetAddrTagList'
-            )
+                'snmpTargetAddrTagList')
 
-            self.__emptyTag = SnmpTagValue('')
+            self._emptyTag = SnmpTagValue('')
 
-            self.__transportToTagMap = {}
+            self._transportToTagMap = {}
 
             nextMibNode = snmpTargetAddrTagList
 
@@ -151,56 +161,64 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                     break
 
                 instId = nextMibNode.name[len(snmpTargetAddrTagList.name):]
-                targetAddrTDomain = snmpTargetAddrTDomain.getNode(snmpTargetAddrTDomain.name + instId).syntax
-                targetAddrTAddress = snmpTargetAddrTAddress.getNode(snmpTargetAddrTAddress.name + instId).syntax
+
+                targetAddrTDomain = snmpTargetAddrTDomain.getNode(
+                    snmpTargetAddrTDomain.name + instId).syntax
+                targetAddrTAddress = snmpTargetAddrTAddress.getNode(
+                    snmpTargetAddrTAddress.name + instId).syntax
 
                 targetAddrTDomain = tuple(targetAddrTDomain)
 
-                if targetAddrTDomain[:len(udp.SNMP_UDP_DOMAIN)] == udp.SNMP_UDP_DOMAIN:
-                    SnmpUDPAddress, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMPv2-TM',
-                                                                                                            'SnmpUDPAddress')
+                if (targetAddrTDomain[:len(udp.SNMP_UDP_DOMAIN)] ==
+                        udp.SNMP_UDP_DOMAIN):
+                    SnmpUDPAddress, = mibBuilder.importSymbols(
+                        'SNMPv2-TM', 'SnmpUDPAddress')
                     targetAddrTAddress = tuple(SnmpUDPAddress(targetAddrTAddress))
-                elif targetAddrTDomain[:len(udp6.SNMP_UDP6_DOMAIN)] == udp6.SNMP_UDP6_DOMAIN:
-                    TransportAddressIPv6, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+
+                elif (targetAddrTDomain[:len(udp6.SNMP_UDP6_DOMAIN)] ==
+                        udp6.SNMP_UDP6_DOMAIN):
+                    TransportAddressIPv6, = mibBuilder.importSymbols(
                         'TRANSPORT-ADDRESS-MIB', 'TransportAddressIPv6')
+
                     targetAddrTAddress = tuple(TransportAddressIPv6(targetAddrTAddress))
 
                 targetAddr = targetAddrTDomain, targetAddrTAddress
-                targetAddrTagList = snmpTargetAddrTagList.getNode(snmpTargetAddrTagList.name + instId).syntax
 
-                if targetAddr not in self.__transportToTagMap:
-                    self.__transportToTagMap[targetAddr] = set()
+                targetAddrTagList = snmpTargetAddrTagList.getNode(
+                    snmpTargetAddrTagList.name + instId).syntax
+
+                if targetAddr not in self._transportToTagMap:
+                    self._transportToTagMap[targetAddr] = set()
 
                 try:
                     if targetAddrTagList:
-                        self.__transportToTagMap[targetAddr].update(
+                        self._transportToTagMap[targetAddr].update(
                             [SnmpTagValue(x)
-                             for x in targetAddrTagList.asOctets().split()]
-                        )
+                             for x in targetAddrTagList.asOctets().split()])
 
                     else:
-                        self.__transportToTagMap[targetAddr].add(self.__emptyTag)
+                        self._transportToTagMap[targetAddr].add(self._emptyTag)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
                         '_com2sec: table entries %r/%r hashing failed' % (
-                            targetAddr, targetAddrTagList)
-                    )
+                            targetAddr, targetAddrTagList))
                     continue
 
-            self.__transportBranchId = snmpTargetAddrTAddress.branchVersionId
+            self._transportBranchId = snmpTargetAddrTAddress.branchVersionId
 
-            debug.logger & debug.FLAG_SM and debug.logger('_com2sec: built transport-to-tag map version %s: %s' % (
-                self.__transportBranchId, self.__transportToTagMap))
+            debug.logger & debug.FLAG_SM and debug.logger(
+                '_com2sec: built transport-to-tag map version %s: '
+                '%s' % (self._transportBranchId, self._transportToTagMap))
 
-        snmpTargetParamsSecurityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        snmpTargetParamsSecurityName, = mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityName')
 
-        if self.__paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
-            snmpTargetParamsSecurityModel, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        if self._paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
+            snmpTargetParamsSecurityModel, = mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityModel')
 
-            self.__nameToModelMap = {}
+            self._nameToModelMap = {}
 
             nextMibNode = snmpTargetParamsSecurityName
 
@@ -213,43 +231,44 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 instId = nextMibNode.name[len(snmpTargetParamsSecurityName.name):]
 
-                mibNode = snmpTargetParamsSecurityModel.getNode(snmpTargetParamsSecurityModel.name + instId)
+                mibNode = snmpTargetParamsSecurityModel.getNode(
+                    snmpTargetParamsSecurityModel.name + instId)
 
                 try:
-                    if nextMibNode.syntax not in self.__nameToModelMap:
-                        self.__nameToModelMap[nextMibNode.syntax] = set()
+                    if nextMibNode.syntax not in self._nameToModelMap:
+                        self._nameToModelMap[nextMibNode.syntax] = set()
 
-                    self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
+                    self._nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_com2sec: table entries %r/%r hashing failed' % (
-                            nextMibNode.syntax, mibNode.syntax)
-                    )
+                        '_com2sec: table entries %r/%r hashing '
+                        'failed' % (nextMibNode.syntax, mibNode.syntax))
                     continue
 
-            self.__paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
+            self._paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
 
             # invalidate next map as it include this one
-            self.__communityBranchId = -1
+            self._communityBranchId = -1
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_com2sec: built securityName to securityModel map, version %s: %s' % (
-                    self.__paramsBranchId, self.__nameToModelMap))
+                '_com2sec: built securityName to securityModel map, version '
+                '%s: %s' % (self._paramsBranchId, self._nameToModelMap))
+
+        snmpCommunityName, = mibBuilder.importSymbols(
+            'SNMP-COMMUNITY-MIB', 'snmpCommunityName')
 
-        snmpCommunityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMP-COMMUNITY-MIB',
-                                                                                                   'snmpCommunityName')
-        if self.__communityBranchId != snmpCommunityName.branchVersionId:
+        if self._communityBranchId != snmpCommunityName.branchVersionId:
             (snmpCommunitySecurityName, snmpCommunityContextEngineId,
              snmpCommunityContextName,
-             snmpCommunityTransportTag) = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+             snmpCommunityTransportTag) = mibBuilder.importSymbols(
                 'SNMP-COMMUNITY-MIB', 'snmpCommunitySecurityName',
                 'snmpCommunityContextEngineID', 'snmpCommunityContextName',
                 'snmpCommunityTransportTag'
             )
 
-            self.__communityToTagMap = {}
-            self.__tagAndCommunityToSecurityMap = {}
+            self._communityToTagMap = {}
+            self._tagAndCommunityToSecurityMap = {}
 
             nextMibNode = snmpCommunityName
 
@@ -262,100 +281,125 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 instId = nextMibNode.name[len(snmpCommunityName.name):]
 
-                securityName = snmpCommunitySecurityName.getNode(snmpCommunitySecurityName.name + instId).syntax
+                securityName = snmpCommunitySecurityName.getNode(
+                    snmpCommunitySecurityName.name + instId).syntax
 
                 contextEngineId = snmpCommunityContextEngineId.getNode(
                     snmpCommunityContextEngineId.name + instId).syntax
 
-                contextName = snmpCommunityContextName.getNode(snmpCommunityContextName.name + instId).syntax
+                contextName = snmpCommunityContextName.getNode(
+                    snmpCommunityContextName.name + instId).syntax
 
-                transportTag = snmpCommunityTransportTag.getNode(snmpCommunityTransportTag.name + instId).syntax
+                transportTag = snmpCommunityTransportTag.getNode(
+                    snmpCommunityTransportTag.name + instId).syntax
 
                 _tagAndCommunity = transportTag, nextMibNode.syntax
 
                 try:
-                    if _tagAndCommunity not in self.__tagAndCommunityToSecurityMap:
-                        self.__tagAndCommunityToSecurityMap[_tagAndCommunity] = set()
+                    if _tagAndCommunity not in self._tagAndCommunityToSecurityMap:
+                        self._tagAndCommunityToSecurityMap[_tagAndCommunity] = set()
 
-                    self.__tagAndCommunityToSecurityMap[_tagAndCommunity].add(
-                        (securityName, contextEngineId, contextName)
-                    )
+                    self._tagAndCommunityToSecurityMap[_tagAndCommunity].add(
+                        (securityName, contextEngineId, contextName))
 
-                    if nextMibNode.syntax not in self.__communityToTagMap:
-                        self.__communityToTagMap[nextMibNode.syntax] = set()
+                    if nextMibNode.syntax not in self._communityToTagMap:
+                        self._communityToTagMap[nextMibNode.syntax] = set()
 
-                    self.__communityToTagMap[nextMibNode.syntax].add(transportTag)
+                    self._communityToTagMap[nextMibNode.syntax].add(transportTag)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_com2sec: table entries %r/%r hashing failed' % (
-                            _tagAndCommunity, nextMibNode.syntax)
-                    )
+                        '_com2sec: table entries %r/%r hashing '
+                        'failed' % (_tagAndCommunity, nextMibNode.syntax))
                     continue
 
-            self.__communityBranchId = snmpCommunityName.branchVersionId
+            self._communityBranchId = snmpCommunityName.branchVersionId
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_com2sec: built communityName to tag map (securityModel %s), version %s: %s' % (
-                    self.SECURITY_MODEL_ID, self.__communityBranchId, self.__communityToTagMap))
+                '_com2sec: built communityName to tag map '
+                '(securityModel %s), version %s: '
+                '%s' % (self.SECURITY_MODEL_ID, self._communityBranchId,
+                        self._communityToTagMap))
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_com2sec: built tag & community to securityName map (securityModel %s), version %s: %s' % (
-                    self.SECURITY_MODEL_ID, self.__communityBranchId, self.__tagAndCommunityToSecurityMap))
-
-        if communityName in self.__communityToTagMap:
-            if transportInformation in self.__transportToTagMap:
-                tags = self.__transportToTagMap[transportInformation].intersection(
-                    self.__communityToTagMap[communityName])
-            elif self.__emptyTag in self.__communityToTagMap[communityName]:
-                tags = [self.__emptyTag]
+                '_com2sec: built tag & community to securityName map '
+                '(securityModel %s), version %s: '
+                '%s' % (self.SECURITY_MODEL_ID, self._communityBranchId,
+                        self._tagAndCommunityToSecurityMap))
+
+        if communityName in self._communityToTagMap:
+            if transportInformation in self._transportToTagMap:
+                tags = self._transportToTagMap[transportInformation].intersection(
+                    self._communityToTagMap[communityName])
+
+            elif self._emptyTag in self._communityToTagMap[communityName]:
+                tags = [self._emptyTag]
+
             else:
-                raise error.StatusInformation(errorIndication=errind.unknownCommunityName)
+                raise error.StatusInformation(
+                    errorIndication=errind.unknownCommunityName)
 
             candidateSecurityNames = []
 
-            for x in [self.__tagAndCommunityToSecurityMap[(t, communityName)] for t in tags]:
+            securityNamesSets = [
+                self._tagAndCommunityToSecurityMap[(t, communityName)]
+                for t in tags
+            ]
+
+            for x in securityNamesSets:
                 candidateSecurityNames.extend(list(x))
 
-            # 5.2.1 (row selection in snmpCommunityTable)
-            # Picks first match but favors entries already in targets table
             if candidateSecurityNames:
-                candidateSecurityNames.sort(
-                    key=lambda x, m=self.__nameToModelMap, v=self.SECURITY_MODEL_ID: (
-                        not int(x[0] in m and v in m[x[0]]), str(x[0]))
-                )
+                candidateSecurityNames.sort(key=self._orderSecurityNames)
+
                 chosenSecurityName = candidateSecurityNames[0]  # min()
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '_com2sec: securityName candidates for communityName \'%s\' are %s; choosing securityName \'%s\'' % (
-                        communityName, candidateSecurityNames, chosenSecurityName[0]))
+                    '_com2sec: securityName candidates for communityName %s '
+                    'are %s; choosing securityName '
+                    '%s' % (communityName, candidateSecurityNames,
+                            chosenSecurityName[0]))
+
                 return chosenSecurityName
 
-        raise error.StatusInformation(errorIndication=errind.unknownCommunityName)
+        raise error.StatusInformation(
+            errorIndication=errind.unknownCommunityName)
+
+    # 5.2.1 (row selection in snmpCommunityTable)
+    # Picks first match but favors entries already in targets table
+    def _orderSecurityNames(self, securityName):
+        return (not int(securityName[0] in self._nameToModelMap and
+                        self.SECURITY_MODEL_ID in self._nameToModelMap[securityName[0]]),
+                str(securityName[0]))
 
     def generateRequestMsg(self, snmpEngine, messageProcessingModel,
                            globalData, maxMessageSize, securityModel,
                            securityEngineId, securityName, securityLevel,
                            scopedPDU):
         msg, = globalData
+
         contextEngineId, contextName, pdu = scopedPDU
 
         # rfc2576: 5.2.3
-        communityName = self._sec2com(snmpEngine, securityName,
-                                      contextEngineId, contextName)
+        communityName = self._sec2com(
+            snmpEngine, securityName, contextEngineId, contextName)
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'generateRequestMsg: using community %r for securityModel %r, securityName %r, contextEngineId %r contextName %r' % (
-                communityName, securityModel, securityName, contextEngineId, contextName))
+            'generateRequestMsg: using community %r for securityModel %r, '
+            'securityName %r, contextEngineId %r contextName '
+            '%r' % (communityName, securityModel, securityName,
+                    contextEngineId, contextName))
 
         securityParameters = communityName
 
         msg.setComponentByPosition(1, securityParameters)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        debug.logger & debug.FLAG_MP and debug.logger('generateRequestMsg: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'generateRequestMsg: %s' % (msg.prettyPrint(),))
 
         try:
             return securityParameters, encoder.encode(msg)
@@ -363,7 +407,9 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
         except PyAsn1Error as exc:
             debug.logger & debug.FLAG_MP and debug.logger(
                 'generateRequestMsg: serialization failure: %s' % exc)
-            raise error.StatusInformation(errorIndication=errind.serializationError)
+
+            raise error.StatusInformation(
+                errorIndication=errind.serializationError)
 
     def generateResponseMsg(self, snmpEngine, messageProcessingModel,
                             globalData, maxMessageSize, securityModel,
@@ -371,21 +417,26 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                             scopedPDU, securityStateReference):
         # rfc2576: 5.2.2
         msg, = globalData
+
         contextEngineId, contextName, pdu = scopedPDU
+
         cachedSecurityData = self._cache.pop(securityStateReference)
+
         communityName = cachedSecurityData['communityName']
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'generateResponseMsg: recovered community %r by securityStateReference %s' % (
-                communityName, securityStateReference))
+            'generateResponseMsg: recovered community %r by '
+            'securityStateReference '
+            '%s' % (communityName, securityStateReference))
 
         msg.setComponentByPosition(1, communityName)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        debug.logger & debug.FLAG_MP and debug.logger('generateResponseMsg: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'generateResponseMsg: %s' % (msg.prettyPrint(),))
 
         try:
             return communityName, encoder.encode(msg)
@@ -393,11 +444,14 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
         except PyAsn1Error as exc:
             debug.logger & debug.FLAG_MP and debug.logger(
                 'generateResponseMsg: serialization failure: %s' % exc)
+
             raise error.StatusInformation(errorIndication=errind.serializationError)
 
     def processIncomingMsg(self, snmpEngine, messageProcessingModel,
                            maxMessageSize, securityParameters, securityModel,
                            securityLevel, wholeMsg, msg):
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
         # rfc2576: 5.2.1
         communityName, transportInformation = securityParameters
 
@@ -407,6 +461,7 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
         snmpEngine.observer.storeExecutionContext(
             snmpEngine, 'rfc2576.processIncomingMsg:writable', scope
         )
+
         snmpEngine.observer.clearExecutionContext(
             snmpEngine, 'rfc2576.processIncomingMsg:writable'
         )
@@ -418,16 +473,17 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
             )
 
         except error.StatusInformation:
-            snmpInBadCommunityNames, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+            snmpInBadCommunityNames, = mibBuilder.importSymbols(
                 '__SNMPv2-MIB', 'snmpInBadCommunityNames')
             snmpInBadCommunityNames.syntax += 1
+
             raise error.StatusInformation(
                 errorIndication=errind.unknownCommunityName,
                 communityName=communityName
             )
 
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                              'snmpEngineID')
+        snmpEngineID, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
         securityEngineID = snmpEngineID.syntax
 
@@ -440,24 +496,31 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                  contextEngineId=contextEngineId,
                  contextName=contextName)
         )
+
         snmpEngine.observer.clearExecutionContext(
             snmpEngine, 'rfc2576.processIncomingMsg'
         )
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: looked up securityName %r securityModel %r contextEngineId %r contextName %r by communityName %r AND transportInformation %r' % (
-                securityName, self.SECURITY_MODEL_ID, contextEngineId, contextName, communityName, transportInformation))
+            'processIncomingMsg: looked up securityName %r securityModel %r '
+            'contextEngineId %r contextName %r by communityName %r '
+            'AND transportInformation '
+            '%r' % (securityName, self.SECURITY_MODEL_ID, contextEngineId,
+                    contextName, communityName, transportInformation))
 
         stateReference = self._cache.push(communityName=communityName)
 
         scopedPDU = (contextEngineId, contextName,
                      msg.getComponentByPosition(2).getComponent())
+
         maxSizeResponseScopedPDU = maxMessageSize - 128
+
         securityStateReference = stateReference
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: generated maxSizeResponseScopedPDU %s securityStateReference %s' % (
-                maxSizeResponseScopedPDU, securityStateReference))
+            'processIncomingMsg: generated maxSizeResponseScopedPDU '
+            '%s securityStateReference '
+            '%s' % (maxSizeResponseScopedPDU, securityStateReference))
 
         return (securityEngineID, securityName, scopedPDU,
                 maxSizeResponseScopedPDU, securityStateReference)
diff --git a/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py b/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py
index df3db63f..c3578682 100644
--- a/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py
+++ b/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py
@@ -41,11 +41,13 @@ class HmacMd5(base.AbstractAuthenticationService):
         # should be in the substrate. Also, it pre-sets digest placeholder
         # so we hash wholeMsg out of the box.
         # Yes, that's ugly but that's rfc...
-        l = wholeMsg.find(TWELVE_ZEROS)
-        if l == -1:
+        ln = wholeMsg.find(TWELVE_ZEROS)
+
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest placeholder')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
 
         # 6.3.1.1
 
@@ -56,15 +58,13 @@ class HmacMd5(base.AbstractAuthenticationService):
 
         # 6.3.1.2c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 6.3.1.2d --> no-op
 
         # 6.3.1.2e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 6.3.1.3
         # noinspection PyDeprecation,PyCallingNonCallable
@@ -83,15 +83,16 @@ class HmacMd5(base.AbstractAuthenticationService):
         # 6.3.2.1 & 2
         if len(authParameters) != 12:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationError
-            )
+                errorIndication=errind.authenticationError)
 
         # 6.3.2.3
-        l = wholeMsg.find(authParameters.asOctets())
-        if l == -1:
+        ln = wholeMsg.find(authParameters.asOctets())
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest in wholeMsg')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
+
         authenticatedWholeMsg = wholeHead + TWELVE_ZEROS + wholeTail
 
         # 6.3.2.4a
@@ -101,15 +102,13 @@ class HmacMd5(base.AbstractAuthenticationService):
 
         # 6.3.2.4c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 6.3.2.4d --> no-op
 
         # 6.3.2.4e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 6.3.2.5a
         # noinspection PyDeprecation,PyCallingNonCallable
@@ -125,7 +124,6 @@ class HmacMd5(base.AbstractAuthenticationService):
         # 6.3.2.6
         if mac != authParameters:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationFailure
-            )
+                errorIndication=errind.authenticationFailure)
 
         return authenticatedWholeMsg
diff --git a/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py b/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py
index 4d5498d1..76c35af0 100644
--- a/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py
+++ b/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py
@@ -42,11 +42,12 @@ class HmacSha(base.AbstractAuthenticationService):
         # should be in the substrate. Also, it pre-sets digest placeholder
         # so we hash wholeMsg out of the box.
         # Yes, that's ugly but that's rfc...
-        l = wholeMsg.find(TWELVE_ZEROS)
-        if l == -1:
+        ln = wholeMsg.find(TWELVE_ZEROS)
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest placeholder')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
 
         # 7.3.1.2a
         extendedAuthKey = authKey.asNumbers() + FORTY_FOUR_ZEROS
@@ -55,15 +56,13 @@ class HmacSha(base.AbstractAuthenticationService):
 
         # 7.3.1.2c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 7.3.1.2d -- no-op
 
         # 7.3.1.2e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 7.3.1.3
         d1 = sha1(k1.asOctets() + wholeMsg).digest()
@@ -80,15 +79,16 @@ class HmacSha(base.AbstractAuthenticationService):
         # 7.3.2.1 & 2
         if len(authParameters) != 12:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationError
-            )
+                errorIndication=errind.authenticationError)
 
         # 7.3.2.3
-        l = wholeMsg.find(authParameters.asOctets())
-        if l == -1:
+        ln = wholeMsg.find(authParameters.asOctets())
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest in wholeMsg')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
+
         authenticatedWholeMsg = wholeHead + TWELVE_ZEROS + wholeTail
 
         # 7.3.2.4a
@@ -98,15 +98,13 @@ class HmacSha(base.AbstractAuthenticationService):
 
         # 7.3.2.4c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 7.3.2.4d --> no-op
 
         # 7.3.2.4e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 7.3.2.5a
         d1 = sha1(k1.asOctets() + authenticatedWholeMsg).digest()
@@ -120,7 +118,6 @@ class HmacSha(base.AbstractAuthenticationService):
         # 7.3.2.6
         if mac != authParameters:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationFailure
-            )
+                errorIndication=errind.authenticationFailure)
 
         return authenticatedWholeMsg
diff --git a/pysnmp/proto/secmod/rfc3414/localkey.py b/pysnmp/proto/secmod/rfc3414/localkey.py
index 144342fa..bc4faa91 100644
--- a/pysnmp/proto/secmod/rfc3414/localkey.py
+++ b/pysnmp/proto/secmod/rfc3414/localkey.py
@@ -12,9 +12,12 @@ from pyasn1.type import univ
 
 def hashPassphrase(passphrase, hashFunc):
     passphrase = univ.OctetString(passphrase).asOctets()
+
     hasher = hashFunc()
+
     ringBuffer = passphrase * (64 // len(passphrase) + 1)
     ringBufferLen = len(ringBuffer)
+
     count = 0
     mark = 0
 
@@ -25,9 +28,11 @@ def hashPassphrase(passphrase, hashFunc):
             mark = e
 
         else:
-            hasher.update(
-                ringBuffer[mark:ringBufferLen] + ringBuffer[0:e - ringBufferLen]
-            )
+            chunk = ringBuffer[mark:ringBufferLen]
+            chunk += ringBuffer[0:e - ringBufferLen]
+
+            hasher.update(chunk)
+
             mark = e - ringBufferLen
 
         count += 1
@@ -36,11 +41,13 @@ def hashPassphrase(passphrase, hashFunc):
 
 
 def passwordToKey(passphrase, snmpEngineId, hashFunc):
-    return localizeKey(hashPassphrase(passphrase, hashFunc), snmpEngineId, hashFunc)
+    return localizeKey(
+        hashPassphrase(passphrase, hashFunc), snmpEngineId, hashFunc)
 
 
 def localizeKey(passKey, snmpEngineId, hashFunc):
     passKey = univ.OctetString(passKey).asOctets()
+
     # noinspection PyDeprecation,PyCallingNonCallable
     return hashFunc(passKey + snmpEngineId.asOctets() + passKey).digest()
 
diff --git a/pysnmp/proto/secmod/rfc3414/priv/des.py b/pysnmp/proto/secmod/rfc3414/priv/des.py
index 5128a662..10058aeb 100644
--- a/pysnmp/proto/secmod/rfc3414/priv/des.py
+++ b/pysnmp/proto/secmod/rfc3414/priv/des.py
@@ -38,32 +38,39 @@ class Des(base.AbstractEncryptionService):
     def hashPassphrase(self, authProtocol, privKey):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         return localkey.hashPassphrase(privKey, hashAlgo)
 
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
+
         return localPrivKey[:self.KEY_SIZE]
 
     # 8.1.1.1
-    def __getEncryptionKey(self, privKey, snmpEngineBoots):
+    def _getEncryptionKey(self, privKey, snmpEngineBoots):
         desKey = privKey[:8]
         preIV = privKey[8:16]
 
@@ -77,42 +84,47 @@ class Des(base.AbstractEncryptionService):
                 self.local_int >> 16 & 0xff,
                 self.local_int >> 8 & 0xff,
                 self.local_int & 0xff]
+
         if self.local_int == 0xffffffff:
             self.local_int = 0
+
         else:
             self.local_int += 1
 
+        iv = map(lambda x, y: x ^ y, salt, preIV.asNumbers())
+
         return (desKey.asOctets(),
                 univ.OctetString(salt).asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt, preIV.asNumbers())).asOctets())
+                univ.OctetString(iv).asOctets())
 
     @staticmethod
-    def __getDecryptionKey(privKey, salt):
-        return (privKey[:8].asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt.asNumbers(), privKey[8:16].asNumbers())).asOctets())
+    def _getDecryptionKey(privKey, salt):
+        iv = map(lambda x, y: x ^ y, salt.asNumbers(),
+                 privKey[8:16].asNumbers())
+
+        return privKey[:8].asOctets(), univ.OctetString(iv).asOctets()
 
     # 8.2.4.1
     def encryptData(self, encryptKey, privParameters, dataToEncrypt):
         snmpEngineBoots, snmpEngineTime, salt = privParameters
 
         # 8.3.1.1
-        desKey, salt, iv = self.__getEncryptionKey(
-            encryptKey, snmpEngineBoots
-        )
+        desKey, salt, iv = self._getEncryptionKey(encryptKey, snmpEngineBoots)
 
         # 8.3.1.2
         privParameters = univ.OctetString(salt)
 
         # 8.1.1.2
-        plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
+        plaintext = dataToEncrypt
+        plaintext += univ.OctetString(
+            (0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
 
         try:
             ciphertext = des.encrypt(plaintext, desKey, iv)
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         # 8.3.1.3 & 4
         return univ.OctetString(ciphertext), privParameters
@@ -124,19 +136,17 @@ class Des(base.AbstractEncryptionService):
         # 8.3.2.1
         if len(salt) != 8:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         # 8.3.2.2 no-op
 
         # 8.3.2.3
-        desKey, iv = self.__getDecryptionKey(decryptKey, salt)
+        desKey, iv = self._getDecryptionKey(decryptKey, salt)
 
         # 8.3.2.4 -> 8.1.1.3
         if len(encryptedData) % 8 != 0:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         try:
             # 8.3.2.6
@@ -144,5 +154,4 @@ class Des(base.AbstractEncryptionService):
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
diff --git a/pysnmp/proto/secmod/rfc3414/service.py b/pysnmp/proto/secmod/rfc3414/service.py
index f9bf056b..0a8f54e5 100644
--- a/pysnmp/proto/secmod/rfc3414/service.py
+++ b/pysnmp/proto/secmod/rfc3414/service.py
@@ -38,15 +38,26 @@ from pysnmp.smi.error import NoSuchInstanceError
 
 class UsmSecurityParameters(rfc1155.TypeCoercionHackMixIn, univ.Sequence):
     componentType = namedtype.NamedTypes(
-        namedtype.NamedType('msgAuthoritativeEngineId', univ.OctetString()),
-        namedtype.NamedType('msgAuthoritativeEngineBoots',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
-        namedtype.NamedType('msgAuthoritativeEngineTime',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
-        namedtype.NamedType('msgUserName',
-                            univ.OctetString().subtype(subtypeSpec=constraint.ValueSizeConstraint(0, 32))),
-        namedtype.NamedType('msgAuthenticationParameters', univ.OctetString()),
-        namedtype.NamedType('msgPrivacyParameters', univ.OctetString())
+        namedtype.NamedType(
+            'msgAuthoritativeEngineId', univ.OctetString()),
+        namedtype.NamedType(
+            'msgAuthoritativeEngineBoots',
+            univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgAuthoritativeEngineTime',
+            univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgUserName',
+            univ.OctetString().subtype(
+                subtypeSpec=constraint.ValueSizeConstraint(0, 32))),
+        namedtype.NamedType(
+            'msgAuthenticationParameters',
+            univ.OctetString()),
+        namedtype.NamedType(
+            'msgPrivacyParameters',
+            univ.OctetString())
     )
 
 
@@ -56,10 +67,14 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
     AUTH_SERVICES = {
         hmacmd5.HmacMd5.SERVICE_ID: hmacmd5.HmacMd5(),
         hmacsha.HmacSha.SERVICE_ID: hmacsha.HmacSha(),
-        hmacsha2.HmacSha2.SHA224_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA224_SERVICE_ID),
-        hmacsha2.HmacSha2.SHA256_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA256_SERVICE_ID),
-        hmacsha2.HmacSha2.SHA384_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA384_SERVICE_ID),
-        hmacsha2.HmacSha2.SHA512_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA512_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA224_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA224_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA256_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA256_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA384_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA384_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA512_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA512_SERVICE_ID),
         noauth.NoAuth.SERVICE_ID: noauth.NoAuth(),
     }
 
@@ -76,21 +91,23 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
     def __init__(self):
         AbstractSecurityModel.__init__(self)
-        self.__securityParametersSpec = UsmSecurityParameters()
-        self.__timeline = {}
-        self.__timelineExpQueue = {}
-        self.__expirationTimer = 0
-        self.__paramsBranchId = -1
+        self._securityParametersSpec = UsmSecurityParameters()
+        self._timeline = {}
+        self._timelineExpQueue = {}
+        self._expirationTimer = 0
+        self._paramsBranchId = -1
 
-    def __sec2usr(self, snmpEngine, securityName, securityEngineID=None):
+    def _sec2usr(self, snmpEngine, securityName, securityEngineID=None):
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
-        usmUserEngineID, = mibBuilder.importSymbols('SNMP-USER-BASED-SM-MIB',
-                                                    'usmUserEngineID')
-        if self.__paramsBranchId != usmUserEngineID.branchVersionId:
+
+        usmUserEngineID, = mibBuilder.importSymbols(
+            'SNMP-USER-BASED-SM-MIB', 'usmUserEngineID')
+
+        if self._paramsBranchId != usmUserEngineID.branchVersionId:
             usmUserName, usmUserSecurityName = mibBuilder.importSymbols(
                 'SNMP-USER-BASED-SM-MIB', 'usmUserName', 'usmUserSecurityName')
 
-            self.__securityToUserMap = {}
+            self._securityToUserMap = {}
 
             nextMibNode = usmUserEngineID
 
@@ -99,108 +116,138 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     nextMibNode = usmUserEngineID.getNextNode(nextMibNode.name)
 
                 except NoSuchInstanceError:
-                    self.__paramsBranchId = usmUserEngineID.branchVersionId
+                    self._paramsBranchId = usmUserEngineID.branchVersionId
+
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_sec2usr: built snmpEngineId + securityName to userName map, version %s: %r' % (
-                            self.__paramsBranchId, self.__securityToUserMap))
+                        '_sec2usr: built snmpEngineId + securityName to '
+                        'userName map, version %s: %r' % (
+                            self._paramsBranchId, self._securityToUserMap))
                     break
 
                 instId = nextMibNode.name[len(usmUserSecurityName.name):]
 
-                __engineID = usmUserEngineID.getNode(usmUserEngineID.name + instId).syntax
-                __userName = usmUserName.getNode(usmUserName.name + instId).syntax
-                __securityName = usmUserSecurityName.getNode(usmUserSecurityName.name + instId).syntax
+                _engineID = usmUserEngineID.getNode(
+                    usmUserEngineID.name + instId).syntax
+                _userName = usmUserName.getNode(
+                    usmUserName.name + instId).syntax
+                _securityName = usmUserSecurityName.getNode(
+                    usmUserSecurityName.name + instId).syntax
 
-                k = __engineID, __securityName
+                k = _engineID, _securityName
 
                 # first (lesser) securityName wins
-                if k not in self.__securityToUserMap:
-                    self.__securityToUserMap[k] = __userName
+                if k not in self._securityToUserMap:
+                    self._securityToUserMap[k] = _userName
 
         if securityEngineID is None:
-            snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+            snmpEngineID, = mibBuilder.importSymbols(
+                '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
             securityEngineID = snmpEngineID.syntax
 
         try:
-            userName = self.__securityToUserMap[(securityEngineID, securityName)]
+            userName = self._securityToUserMap[(securityEngineID, securityName)]
+
         except KeyError:
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_sec2usr: no entry exists for snmpEngineId %r, securityName %r' % (securityEngineID, securityName))
+                '_sec2usr: no entry exists for snmpEngineId %r, securityName '
+                '%r' % (securityEngineID, securityName))
             raise NoSuchInstanceError()  # emulate MIB lookup
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            '_sec2usr: using userName %r for snmpEngineId %r, securityName %r' % (
-                userName, securityEngineID, securityName))
+            '_sec2usr: using userName %r for snmpEngineId %r, securityName '
+            '%r' % (userName, securityEngineID, securityName))
 
         return userName
 
     @staticmethod
-    def __getUserInfo(mibInstrumController, securityEngineID, userName):
-        usmUserEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry'
-        )
+    def _getUserInfo(mibInstrumController, securityEngineID, userName):
+        mibBuilder = mibInstrumController.mibBuilder
+
+        usmUserEntry, = mibBuilder.importSymbols(
+            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry')
+
         tblIdx = usmUserEntry.getInstIdFromIndices(securityEngineID, userName)
+
         # Get userName & securityName
         usmUserName = usmUserEntry.getNode(usmUserEntry.name + (2,) + tblIdx).syntax
         usmUserSecurityName = usmUserEntry.getNode(usmUserEntry.name + (3,) + tblIdx).syntax
+
         # Get protocols
         usmUserAuthProtocol = usmUserEntry.getNode(usmUserEntry.name + (5,) + tblIdx).syntax
         usmUserPrivProtocol = usmUserEntry.getNode(usmUserEntry.name + (8,) + tblIdx).syntax
+
         # Get keys
-        pysnmpUsmKeyEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry'
-        )
-        pysnmpUsmKeyAuthLocalized = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (1,) + tblIdx).syntax
-        pysnmpUsmKeyPrivLocalized = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (2,) + tblIdx).syntax
+        pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
+
+        pysnmpUsmKeyAuthLocalized = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (1,) + tblIdx).syntax
+        pysnmpUsmKeyPrivLocalized = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (2,) + tblIdx).syntax
+
         return (usmUserName, usmUserSecurityName, usmUserAuthProtocol,
                 pysnmpUsmKeyAuthLocalized, usmUserPrivProtocol,
                 pysnmpUsmKeyPrivLocalized)
 
-    def __cloneUserInfo(self, snmpEngine, securityEngineID, userName):
+    def _cloneUserInfo(self, snmpEngine, securityEngineID, userName):
         mibInstrumController = snmpEngine.msgAndPduDsp.mibInstrumController
+        mibBuilder = mibInstrumController.mibBuilder
+
+        snmpEngineID, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
-        snmpEngineID, = mibInstrumController.mibBuilder.importSymbols(
-            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID'
-        )
         # Proto entry
-        usmUserEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry'
-        )
+        usmUserEntry, = mibBuilder.importSymbols(
+            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry')
+
         tblIdx1 = usmUserEntry.getInstIdFromIndices(
-            snmpEngineID.syntax, userName
-        )
+            snmpEngineID.syntax, userName)
+
         # Get proto protocols
-        usmUserName = usmUserEntry.getNode(usmUserEntry.name + (2,) + tblIdx1)
-        usmUserSecurityName = usmUserEntry.getNode(usmUserEntry.name + (3,) + tblIdx1)
-        usmUserCloneFrom = usmUserEntry.getNode(usmUserEntry.name + (4,) + tblIdx1)
-        usmUserAuthProtocol = usmUserEntry.getNode(usmUserEntry.name + (5,) + tblIdx1)
-        usmUserPrivProtocol = usmUserEntry.getNode(usmUserEntry.name + (8,) + tblIdx1)
+        usmUserName = usmUserEntry.getNode(
+            usmUserEntry.name + (2,) + tblIdx1)
+        usmUserSecurityName = usmUserEntry.getNode(
+            usmUserEntry.name + (3,) + tblIdx1)
+        usmUserCloneFrom = usmUserEntry.getNode(
+            usmUserEntry.name + (4,) + tblIdx1)
+        usmUserAuthProtocol = usmUserEntry.getNode(
+            usmUserEntry.name + (5,) + tblIdx1)
+        usmUserPrivProtocol = usmUserEntry.getNode(
+            usmUserEntry.name + (8,) + tblIdx1)
+
         # Get proto keys
-        pysnmpUsmKeyEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry'
-        )
-        pysnmpUsmKeyAuth = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (3,) + tblIdx1)
-        pysnmpUsmKeyPriv = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (4,) + tblIdx1)
+        pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
+
+        pysnmpUsmKeyAuth = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (3,) + tblIdx1)
+        pysnmpUsmKeyPriv = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (4,) + tblIdx1)
 
         # Create new row from proto values
 
-        tblIdx2 = usmUserEntry.getInstIdFromIndices(securityEngineID, userName)
+        tblIdx2 = usmUserEntry.getInstIdFromIndices(
+            securityEngineID, userName)
 
         # New inactive row
         mibInstrumController.writeMibObjects(
-            (usmUserEntry.name + (13,) + tblIdx2, 5), snmpEngine=snmpEngine
-        )
+            (usmUserEntry.name + (13,) + tblIdx2, 5), snmpEngine=snmpEngine)
 
         # Set user&securityNames
-        usmUserEntry.getNode(usmUserEntry.name + (2,) + tblIdx2).syntax = usmUserName.syntax
-        usmUserEntry.getNode(usmUserEntry.name + (3,) + tblIdx2).syntax = usmUserSecurityName.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (2,) + tblIdx2).syntax = usmUserName.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (3,) + tblIdx2).syntax = usmUserSecurityName.syntax
 
         # Store a reference to original row
-        usmUserEntry.getNode(usmUserEntry.name + (4,) + tblIdx2).syntax = usmUserCloneFrom.syntax.clone(tblIdx1)
+        usmUserEntry.getNode(
+            usmUserEntry.name + (4,) + tblIdx2).syntax = usmUserCloneFrom.syntax.clone(tblIdx1)
 
         # Set protocols
-        usmUserEntry.getNode(usmUserEntry.name + (5,) + tblIdx2).syntax = usmUserAuthProtocol.syntax
-        usmUserEntry.getNode(usmUserEntry.name + (8,) + tblIdx2).syntax = usmUserPrivProtocol.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (5,) + tblIdx2).syntax = usmUserAuthProtocol.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (8,) + tblIdx2).syntax = usmUserPrivProtocol.syntax
 
         # Activate row
         mibInstrumController.writeMibObjects(
@@ -208,98 +255,124 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         )
 
         # Localize and set keys
-        pysnmpUsmKeyEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry'
-        )
+        pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
         pysnmpUsmKeyAuthLocalized = pysnmpUsmKeyEntry.getNode(
-            pysnmpUsmKeyEntry.name + (1,) + tblIdx2
-        )
+            pysnmpUsmKeyEntry.name + (1,) + tblIdx2)
+
         if usmUserAuthProtocol.syntax in self.AUTH_SERVICES:
             localizeKey = self.AUTH_SERVICES[usmUserAuthProtocol.syntax].localizeKey
-            localAuthKey = localizeKey(pysnmpUsmKeyAuth.syntax,
-                                       securityEngineID)
+            localAuthKey = localizeKey(
+                pysnmpUsmKeyAuth.syntax, securityEngineID)
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedAuthProtocol
-            )
+                errorIndication=errind.unsupportedAuthProtocol)
+
         if localAuthKey is not None:
             pysnmpUsmKeyAuthLocalized.syntax = pysnmpUsmKeyAuthLocalized.syntax.clone(localAuthKey)
+
         pysnmpUsmKeyPrivLocalized = pysnmpUsmKeyEntry.getNode(
-            pysnmpUsmKeyEntry.name + (2,) + tblIdx2
-        )
+            pysnmpUsmKeyEntry.name + (2,) + tblIdx2)
+
         if usmUserPrivProtocol.syntax in self.PRIV_SERVICES:
             localizeKey = self.PRIV_SERVICES[usmUserPrivProtocol.syntax].localizeKey
-            localPrivKey = localizeKey(usmUserAuthProtocol.syntax,
-                                       pysnmpUsmKeyPriv.syntax,
-                                       securityEngineID)
+            localPrivKey = localizeKey(
+                usmUserAuthProtocol.syntax, pysnmpUsmKeyPriv.syntax,
+                securityEngineID)
+
         else:
-            raise error.StatusInformation(errorIndication=errind.unsupportedPrivProtocol)
+            raise error.StatusInformation(
+                errorIndication=errind.unsupportedPrivProtocol)
+
         if localPrivKey is not None:
             pysnmpUsmKeyPrivLocalized.syntax = pysnmpUsmKeyPrivLocalized.syntax.clone(localPrivKey)
+
         return (usmUserName.syntax, usmUserSecurityName.syntax,
                 usmUserAuthProtocol.syntax, pysnmpUsmKeyAuthLocalized.syntax,
                 usmUserPrivProtocol.syntax, pysnmpUsmKeyPrivLocalized.syntax)
 
-    def __generateRequestOrResponseMsg(self, snmpEngine,
-                                       messageProcessingModel,
-                                       globalData, maxMessageSize,
-                                       securityModel, securityEngineID,
-                                       securityName, securityLevel,
-                                       scopedPDU, securityStateReference):
+    def _generateRequestOrResponseMsg(self, snmpEngine,
+                                      messageProcessingModel,
+                                      globalData, maxMessageSize,
+                                      securityModel, securityEngineID,
+                                      securityName, securityLevel,
+                                      scopedPDU, securityStateReference):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
-        snmpEngineID = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
+
+        snmpEngineID = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
 
         # 3.1.1
         if securityStateReference is not None:
             # 3.1.1a
             cachedSecurityData = self._cache.pop(securityStateReference)
+
             usmUserName = cachedSecurityData['msgUserName']
+
             if 'usmUserSecurityName' in cachedSecurityData:
                 usmUserSecurityName = cachedSecurityData['usmUserSecurityName']
+
             else:
                 usmUserSecurityName = usmUserName
+
             if 'usmUserAuthProtocol' in cachedSecurityData:
                 usmUserAuthProtocol = cachedSecurityData['usmUserAuthProtocol']
+
             else:
                 usmUserAuthProtocol = noauth.NoAuth.SERVICE_ID
+
             if 'usmUserAuthKeyLocalized' in cachedSecurityData:
                 usmUserAuthKeyLocalized = cachedSecurityData['usmUserAuthKeyLocalized']
+
             else:
                 usmUserAuthKeyLocalized = None
+
             if 'usmUserPrivProtocol' in cachedSecurityData:
                 usmUserPrivProtocol = cachedSecurityData['usmUserPrivProtocol']
+
             else:
                 usmUserPrivProtocol = nopriv.NoPriv.SERVICE_ID
+
             if 'usmUserPrivKeyLocalized' in cachedSecurityData:
                 usmUserPrivKeyLocalized = cachedSecurityData['usmUserPrivKeyLocalized']
+
             else:
                 usmUserPrivKeyLocalized = None
+
             securityEngineID = snmpEngineID
-            debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: user info read from cache')
+
+            debug.logger & debug.FLAG_SM and debug.logger(
+                '__generateRequestOrResponseMsg: user info read from cache')
+
         elif securityName:
             # 3.1.1b
             try:
                 (usmUserName, usmUserSecurityName, usmUserAuthProtocol,
                  usmUserAuthKeyLocalized, usmUserPrivProtocol,
-                 usmUserPrivKeyLocalized) = self.__getUserInfo(
+                 usmUserPrivKeyLocalized) = self._getUserInfo(
                     snmpEngine.msgAndPduDsp.mibInstrumController,
                     securityEngineID,
-                    self.__sec2usr(snmpEngine, securityName, securityEngineID)
+                    self._sec2usr(snmpEngine, securityName, securityEngineID)
                 )
-                debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: read user info')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    '__generateRequestOrResponseMsg: read user info')
 
             except NoSuchInstanceError:
-                pysnmpUsmDiscovery, = mibBuilder.importSymbols('__PYSNMP-USM-MIB', 'pysnmpUsmDiscovery')
+                pysnmpUsmDiscovery, = mibBuilder.importSymbols(
+                    '__PYSNMP-USM-MIB', 'pysnmpUsmDiscovery')
+
                 reportUnknownName = not pysnmpUsmDiscovery.syntax
+
                 if not reportUnknownName:
                     try:
                         (usmUserName, usmUserSecurityName,
                          usmUserAuthProtocol, usmUserAuthKeyLocalized,
                          usmUserPrivProtocol,
-                         usmUserPrivKeyLocalized) = self.__cloneUserInfo(
-                            snmpEngine,
-                            securityEngineID,
-                            self.__sec2usr(snmpEngine, securityName)
+                         usmUserPrivKeyLocalized) = self._cloneUserInfo(
+                            snmpEngine, securityEngineID,
+                            self._sec2usr(snmpEngine, securityName)
                         )
 
                     except NoSuchInstanceError:
@@ -307,31 +380,40 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
                 if reportUnknownName:
                     raise error.StatusInformation(
-                        errorIndication=errind.unknownSecurityName
-                    )
+                        errorIndication=errind.unknownSecurityName)
 
-                debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: clone user info')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    '__generateRequestOrResponseMsg: clone user info')
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
                     '__generateRequestOrResponseMsg: %s' % exc)
-                snmpInGenErrs, = mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInGenErrs')
+
+                snmpInGenErrs, = mibBuilder.importSymbols(
+                    '__SNMPv2-MIB', 'snmpInGenErrs')
                 snmpInGenErrs.syntax += 1
-                raise error.StatusInformation(
-                    errorIndication=errind.invalidMsg
-                )
+
+                raise error.StatusInformation(errorIndication=errind.invalidMsg)
+
         else:
             # empty username used for engineID discovery
             usmUserName = usmUserSecurityName = null
             usmUserAuthProtocol = noauth.NoAuth.SERVICE_ID
             usmUserPrivProtocol = nopriv.NoPriv.SERVICE_ID
+
             usmUserAuthKeyLocalized = usmUserPrivKeyLocalized = None
-            debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: use empty USM data')
+
+            debug.logger & debug.FLAG_SM and debug.logger(
+                '__generateRequestOrResponseMsg: use empty USM data')
 
         # noinspection PyUnboundLocalVariable
         debug.logger & debug.FLAG_SM and debug.logger(
-            '__generateRequestOrResponseMsg: local usmUserName %r usmUserSecurityName %r usmUserAuthProtocol %s usmUserPrivProtocol %s securityEngineID %r securityName %r' % (
-                usmUserName, usmUserSecurityName, usmUserAuthProtocol, usmUserPrivProtocol, securityEngineID, securityName))
+            '__generateRequestOrResponseMsg: local usmUserName %r '
+            'usmUserSecurityName %r usmUserAuthProtocol %s '
+            'usmUserPrivProtocol %s securityEngineID %r '
+            'securityName %r' % (
+                usmUserName, usmUserSecurityName, usmUserAuthProtocol,
+                usmUserPrivProtocol, securityEngineID, securityName))
 
         msg = globalData
 
@@ -340,22 +422,21 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             if (usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID or
                     usmUserPrivProtocol == nopriv.NoPriv.SERVICE_ID):
                 raise error.StatusInformation(
-                    errorIndication=errind.unsupportedSecurityLevel
-                )
+                    errorIndication=errind.unsupportedSecurityLevel)
 
         # 3.1.3
         if securityLevel == 3 or securityLevel == 2:
             if usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID:
                 raise error.StatusInformation(
-                    errorIndication=errind.unsupportedSecurityLevel
-                )
+                    errorIndication=errind.unsupportedSecurityLevel)
 
-        securityParameters = self.__securityParametersSpec
+        securityParameters = self._securityParametersSpec
 
         scopedPDUData = msg.setComponentByPosition(3).getComponentByPosition(3)
+
         scopedPDUData.setComponentByPosition(
-            0, scopedPDU, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, scopedPDU, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         snmpEngineBoots = snmpEngineTime = 0
 
@@ -364,161 +445,180 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
             # 3.1.6.b
             if pdu.tagSet in rfc3411.UNCONFIRMED_CLASS_PDUS:
-                (snmpEngineBoots,
-                 snmpEngineTime) = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots', 'snmpEngineTime')
+                snmpEngineBoots, snmpEngineTime = mibBuilder.importSymbols(
+                    '__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots',
+                    'snmpEngineTime')
 
                 snmpEngineBoots = snmpEngineBoots.syntax
                 snmpEngineTime = snmpEngineTime.syntax.clone()
 
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: read snmpEngineBoots, snmpEngineTime from LCD')
+                    '__generateRequestOrResponseMsg: read snmpEngineBoots, '
+                    'snmpEngineTime from LCD')
 
             # 3.1.6a
-            elif securityEngineID in self.__timeline:
+            elif securityEngineID in self._timeline:
                 (snmpEngineBoots,
                  snmpEngineTime,
                  latestReceivedEngineTime,
-                 latestUpdateTimestamp) = self.__timeline[securityEngineID]
+                 latestUpdateTimestamp) = self._timeline[securityEngineID]
 
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: read snmpEngineBoots, snmpEngineTime from timeline')
+                    '__generateRequestOrResponseMsg: read snmpEngineBoots, '
+                    'snmpEngineTime from timeline')
 
             # 3.1.6.c
             else:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: assuming zero snmpEngineBoots, snmpEngineTime')
+                    '__generateRequestOrResponseMsg: assuming zero '
+                    'snmpEngineBoots, snmpEngineTime')
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: use snmpEngineBoots %s snmpEngineTime %s for securityEngineID %r' % (
+                '__generateRequestOrResponseMsg: use snmpEngineBoots %s '
+                'snmpEngineTime %s for securityEngineID %r' % (
                     snmpEngineBoots, snmpEngineTime, securityEngineID))
 
         # 3.1.4a
         if securityLevel == 3:
             if usmUserPrivProtocol in self.PRIV_SERVICES:
                 privHandler = self.PRIV_SERVICES[usmUserPrivProtocol]
+
             else:
                 raise error.StatusInformation(
-                    errorIndication=errind.encryptionError
-                )
+                    errorIndication=errind.encryptionError)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: scopedPDU %s' % scopedPDU.prettyPrint())
+                '__generateRequestOrResponseMsg: scopedPDU '
+                '%s' % scopedPDU.prettyPrint())
 
             try:
                 dataToEncrypt = encoder.encode(scopedPDU)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: scopedPDU serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: scopedPDU serialization '
+                    'error: %s' % exc)
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: scopedPDU encoded into %s' % debug.hexdump(dataToEncrypt))
+                '__generateRequestOrResponseMsg: scopedPDU encoded into '
+                '%s' % debug.hexdump(dataToEncrypt))
 
             # noinspection PyUnboundLocalVariable
-            (encryptedData,
-             privParameters) = privHandler.encryptData(
+            encryptedData, privParameters = privHandler.encryptData(
                 usmUserPrivKeyLocalized,
-                (snmpEngineBoots, snmpEngineTime, None), dataToEncrypt
-            )
+                (snmpEngineBoots, snmpEngineTime, None),
+                dataToEncrypt)
 
             securityParameters.setComponentByPosition(
-                5, privParameters, verifyConstraints=False, matchTags=False, matchConstraints=False
-            )
+                5, privParameters, verifyConstraints=False, matchTags=False,
+                matchConstraints=False)
+
             scopedPDUData.setComponentByPosition(
-                1, encryptedData, verifyConstraints=False, matchTags=False, matchConstraints=False
-            )
+                1, encryptedData, verifyConstraints=False, matchTags=False,
+                matchConstraints=False)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: scopedPDU ciphered into %s' % debug.hexdump(encryptedData))
+                '__generateRequestOrResponseMsg: scopedPDU ciphered into '
+                '%s' % debug.hexdump(encryptedData))
 
         # 3.1.4b
         elif securityLevel == 1 or securityLevel == 2:
             securityParameters.setComponentByPosition(5, '')
 
-        debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: %s' % scopedPDUData.prettyPrint())
+        debug.logger & debug.FLAG_SM and debug.logger(
+            '__generateRequestOrResponseMsg: %s' % scopedPDUData.prettyPrint())
 
         # 3.1.5
         securityParameters.setComponentByPosition(
-            0, securityEngineID, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, securityEngineID, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         securityParameters.setComponentByPosition(
-            1, snmpEngineBoots, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, snmpEngineBoots, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         securityParameters.setComponentByPosition(
-            2, snmpEngineTime, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, snmpEngineTime, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 3.1.7
         securityParameters.setComponentByPosition(
-            3, usmUserName, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            3, usmUserName, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 3.1.8a
         if securityLevel == 3 or securityLevel == 2:
             if usmUserAuthProtocol in self.AUTH_SERVICES:
                 authHandler = self.AUTH_SERVICES[usmUserAuthProtocol]
+
             else:
                 raise error.StatusInformation(
-                    errorIndication=errind.authenticationFailure
-                )
+                    errorIndication=errind.authenticationFailure)
 
             # extra-wild hack to facilitate BER substrate in-place re-write
             securityParameters.setComponentByPosition(
-                4, '\x00' * authHandler.digestLength
-            )
+                4, '\x00' * authHandler.digestLength)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: %s' % (securityParameters.prettyPrint(),))
+                '__generateRequestOrResponseMsg: '
+                '%s' % (securityParameters.prettyPrint(),))
 
             try:
-                msg.setComponentByPosition(2, encoder.encode(securityParameters), verifyConstraints=False)
+                msg.setComponentByPosition(
+                    2, encoder.encode(securityParameters),
+                    verifyConstraints=False)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: securityParameters serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: securityParameters '
+                    'serialization error: %s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: auth outgoing msg: %s' % msg.prettyPrint())
+                '__generateRequestOrResponseMsg: auth outgoing msg: '
+                '%s' % msg.prettyPrint())
 
             try:
                 wholeMsg = encoder.encode(msg)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: msg serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: msg serialization '
+                    'error: %s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             # noinspection PyUnboundLocalVariable
             authenticatedWholeMsg = authHandler.authenticateOutgoingMsg(
-                usmUserAuthKeyLocalized, wholeMsg
-            )
+                usmUserAuthKeyLocalized, wholeMsg)
 
         # 3.1.8b
         else:
             securityParameters.setComponentByPosition(
-                4, '', verifyConstraints=False, matchTags=False, matchConstraints=False
-            )
+                4, '', verifyConstraints=False, matchTags=False,
+                matchConstraints=False)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: %s' % (securityParameters.prettyPrint(),))
+                '__generateRequestOrResponseMsg: '
+                '%s' % (securityParameters.prettyPrint(),))
 
             try:
-                msg.setComponentByPosition(2, encoder.encode(securityParameters), verifyConstraints=False, matchTags=False, matchConstraints=False)
+                msg.setComponentByPosition(
+                    2, encoder.encode(securityParameters), verifyConstraints=False,
+                    matchTags=False, matchConstraints=False)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: secutiryParameters serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: securityParameters '
+                    'serialization error: %s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             try:
                 debug.logger & debug.FLAG_SM and debug.logger(
@@ -527,13 +627,16 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: msg serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: msg serialization error: '
+                    '%s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
-        debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: %s outgoing msg: %s' % (
-            securityLevel > 1 and "authenticated" or "plain", debug.hexdump(authenticatedWholeMsg)))
+        debug.logger & debug.FLAG_SM and debug.logger(
+            '__generateRequestOrResponseMsg: %s outgoing msg: '
+            '%s' % (securityLevel > 1 and "authenticated" or
+                    "plain", debug.hexdump(authenticatedWholeMsg)))
 
         # 3.1.9
         return msg.getComponentByPosition(2), authenticatedWholeMsg
@@ -542,88 +645,99 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                            globalData, maxMessageSize, securityModel,
                            securityEngineID, securityName, securityLevel,
                            scopedPDU):
-        return self.__generateRequestOrResponseMsg(snmpEngine,
-                                                   messageProcessingModel,
-                                                   globalData,
-                                                   maxMessageSize,
-                                                   securityModel,
-                                                   securityEngineID,
-                                                   securityName,
-                                                   securityLevel,
-                                                   scopedPDU,
-                                                   None)
+
+        return self._generateRequestOrResponseMsg(
+            snmpEngine, messageProcessingModel, globalData,
+            maxMessageSize, securityModel, securityEngineID,
+            securityName, securityLevel, scopedPDU, None)
 
     def generateResponseMsg(self, snmpEngine, messageProcessingModel,
                             globalData, maxMessageSize, securityModel,
                             securityEngineID, securityName, securityLevel,
                             scopedPDU, securityStateReference):
-        return self.__generateRequestOrResponseMsg(
+
+        return self._generateRequestOrResponseMsg(
             snmpEngine, messageProcessingModel, globalData,
             maxMessageSize, securityModel, securityEngineID,
-            securityName, securityLevel, scopedPDU, securityStateReference
+            securityName, securityLevel, scopedPDU,
+            securityStateReference
         )
 
     # 3.2
     def processIncomingMsg(self, snmpEngine, messageProcessingModel,
                            maxMessageSize, securityParameters,
                            securityModel, securityLevel, wholeMsg, msg):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
         # 3.2.9 -- moved up here to be able to report
         # maxSizeResponseScopedPDU on error
         # (48 - maximum SNMPv3 header length)
-        maxSizeResponseScopedPDU = int(maxMessageSize) - len(securityParameters) - 48
+        maxSizeResponseScopedPDU = (int(maxMessageSize) -
+                                    len(securityParameters) - 48)
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: securityParameters %s' % debug.hexdump(securityParameters))
+            'processIncomingMsg: securityParameters '
+            '%s' % debug.hexdump(securityParameters))
 
         # 3.2.1
         securityParameters, rest = decoder.decode(
-            securityParameters, asn1Spec=self.__securityParametersSpec
-        )
+            securityParameters, asn1Spec=self._securityParametersSpec)
 
-        debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: %s' % (securityParameters.prettyPrint(),))
+        debug.logger & debug.FLAG_SM and debug.logger(
+            'processIncomingMsg: %s' % (securityParameters.prettyPrint(),))
 
         if eoo.endOfOctets.isSameTypeWith(securityParameters):
             raise error.StatusInformation(errorIndication=errind.parseError)
 
         # 3.2.2
         msgAuthoritativeEngineId = securityParameters.getComponentByPosition(0)
+
         securityStateReference = self._cache.push(
             msgUserName=securityParameters.getComponentByPosition(3)
         )
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: cache write securityStateReference %s by msgUserName %s' % (
-                securityStateReference, securityParameters.getComponentByPosition(3)))
+            'processIncomingMsg: cache write securityStateReference %s by '
+            'msgUserName %s' % (securityStateReference,
+                                securityParameters.getComponentByPosition(3)))
 
         scopedPduData = msg.getComponentByPosition(3)
 
         # Used for error reporting
-        contextEngineId = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
+        contextEngineId = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
         contextName = null
 
-        snmpEngineID = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
+        snmpEngineID = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
 
         # 3.2.3
         if (msgAuthoritativeEngineId != snmpEngineID and
-                msgAuthoritativeEngineId not in self.__timeline):
+                msgAuthoritativeEngineId not in self._timeline):
+
             if (msgAuthoritativeEngineId and
                     4 < len(msgAuthoritativeEngineId) < 33):
                 # 3.2.3a - cloned user when request was sent
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: non-synchronized securityEngineID %r' % (msgAuthoritativeEngineId,))
+                    'processIncomingMsg: non-synchronized securityEngineID '
+                    '%r' % (msgAuthoritativeEngineId,))
+
             else:
                 # 3.2.3b
                 debug.logger & debug.FLAG_SM and debug.logger(
                     'processIncomingMsg: peer requested snmpEngineID discovery')
+
                 usmStatsUnknownEngineIDs, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnknownEngineIDs')
                 usmStatsUnknownEngineIDs.syntax += 1
+
                 debug.logger & debug.FLAG_SM and debug.logger(
                     'processIncomingMsg: null or malformed msgAuthoritativeEngineId')
+
                 pysnmpUsmDiscoverable, = mibBuilder.importSymbols(
                     '__PYSNMP-USM-MIB', 'pysnmpUsmDiscoverable')
+
                 if pysnmpUsmDiscoverable.syntax:
                     debug.logger & debug.FLAG_SM and debug.logger(
                         'processIncomingMsg: starting snmpEngineID discovery procedure')
@@ -631,10 +745,11 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     # Report original contextName
                     if scopedPduData.getName() != 'plaintext':
                         debug.logger & debug.FLAG_SM and debug.logger(
-                            'processIncomingMsg: scopedPduData not plaintext %s' % scopedPduData.prettyPrint())
+                            'processIncomingMsg: scopedPduData not plaintext '
+                            '%s' % scopedPduData.prettyPrint())
+
                         raise error.StatusInformation(
-                            errorIndication=errind.unknownEngineID
-                        )
+                            errorIndication=errind.unknownEngineID)
 
                     # 7.2.6.a.1
                     scopedPdu = scopedPduData.getComponent()
@@ -653,16 +768,18 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                         maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                     )
                 else:
-                    debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: will not discover EngineID')
+                    debug.logger & debug.FLAG_SM and debug.logger(
+                        'processIncomingMsg: will not discover EngineID')
+
                     # free securityStateReference XXX
                     raise error.StatusInformation(
-                        errorIndication=errind.unknownEngineID
-                    )
+                        errorIndication=errind.unknownEngineID)
 
         msgUserName = securityParameters.getComponentByPosition(3)
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: read from securityParams msgAuthoritativeEngineId %r msgUserName %r' % (
+            'processIncomingMsg: read from securityParams '
+            'msgAuthoritativeEngineId %r msgUserName %r' % (
                 msgAuthoritativeEngineId, msgUserName))
 
         if msgUserName:
@@ -673,16 +790,17 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                  usmUserAuthProtocol,
                  usmUserAuthKeyLocalized,
                  usmUserPrivProtocol,
-                 usmUserPrivKeyLocalized) = self.__getUserInfo(
+                 usmUserPrivKeyLocalized) = self._getUserInfo(
                     snmpEngine.msgAndPduDsp.mibInstrumController,
                     msgAuthoritativeEngineId, msgUserName
                 )
-                debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: read user info from LCD')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    'processIncomingMsg: read user info from LCD')
 
             except NoSuchInstanceError:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: unknown securityEngineID %r msgUserName %r' % (
-                        msgAuthoritativeEngineId, msgUserName))
+                    'processIncomingMsg: unknown securityEngineID %r '
+                    'msgUserName %r' % (msgAuthoritativeEngineId, msgUserName))
 
                 usmStatsUnknownUserNames, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnknownUserNames')
@@ -701,10 +819,15 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                 )
 
             except PyAsn1Error as exc:
-                debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: %s' % exc)
-                snmpInGenErrs, = mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInGenErrs')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    'processIncomingMsg: %s' % exc)
+
+                snmpInGenErrs, = mibBuilder.importSymbols(
+                    '__SNMPv2-MIB', 'snmpInGenErrs')
                 snmpInGenErrs.syntax += 1
+
                 raise error.StatusInformation(errorIndication=errind.invalidMsg)
+
         else:
             # empty username used for engineID discovery
             usmUserName = usmUserSecurityName = null
@@ -713,11 +836,14 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             usmUserAuthKeyLocalized = usmUserPrivKeyLocalized = None
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: now have usmUserName %r usmUserSecurityName %r usmUserAuthProtocol %r usmUserPrivProtocol %r for msgUserName %r' % (
-                usmUserName, usmUserSecurityName, usmUserAuthProtocol, usmUserPrivProtocol, msgUserName))
+            'processIncomingMsg: now have usmUserName %r usmUserSecurityName '
+            '%r usmUserAuthProtocol %r usmUserPrivProtocol %r for msgUserName '
+            '%r' % (usmUserName, usmUserSecurityName, usmUserAuthProtocol,
+                    usmUserPrivProtocol, msgUserName))
 
         # 3.2.11 (moved up here to let Reports be authenticated & encrypted)
         self._cache.pop(securityStateReference)
+
         securityStateReference = self._cache.push(
             msgUserName=securityParameters.getComponentByPosition(3),
             usmUserSecurityName=usmUserSecurityName,
@@ -743,21 +869,24 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                  privKey=usmUserPrivKeyLocalized)
         )
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc3414.processIncomingMsg'
-        )
+            snmpEngine, 'rfc3414.processIncomingMsg')
 
         # 3.2.5
         if msgAuthoritativeEngineId == snmpEngineID:
             # Authoritative SNMP engine: make sure securityLevel is sufficient
             badSecIndication = None
+
             if securityLevel == 3:
                 if usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID:
                     badSecIndication = 'authPriv wanted while auth not expected'
+
                 if usmUserPrivProtocol == nopriv.NoPriv.SERVICE_ID:
                     badSecIndication = 'authPriv wanted while priv not expected'
+
             elif securityLevel == 2:
                 if usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID:
                     badSecIndication = 'authNoPriv wanted while auth not expected'
+
                 if usmUserPrivProtocol != nopriv.NoPriv.SERVICE_ID:
                     # 4 (discovery phase always uses authenticated messages)
                     if msgAuthoritativeEngineBoots or msgAuthoritativeEngineTime:
@@ -766,15 +895,20 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             elif securityLevel == 1:
                 if usmUserAuthProtocol != noauth.NoAuth.SERVICE_ID:
                     badSecIndication = 'noAuthNoPriv wanted while auth expected'
+
                 if usmUserPrivProtocol != nopriv.NoPriv.SERVICE_ID:
                     badSecIndication = 'noAuthNoPriv wanted while priv expected'
+
             if badSecIndication:
                 usmStatsUnsupportedSecLevels, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnsupportedSecLevels')
+
                 usmStatsUnsupportedSecLevels.syntax += 1
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: reporting inappropriate security level for user %s: %s' % (
-                        msgUserName, badSecIndication))
+                    'processIncomingMsg: reporting inappropriate security '
+                    'level for user %s: %s' % (msgUserName, badSecIndication))
+
                 raise error.StatusInformation(
                     errorIndication=errind.unsupportedSecurityLevel,
                     oid=usmStatsUnsupportedSecLevels.name,
@@ -791,22 +925,23 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         if securityLevel == 3 or securityLevel == 2:
             if usmUserAuthProtocol in self.AUTH_SERVICES:
                 authHandler = self.AUTH_SERVICES[usmUserAuthProtocol]
+
             else:
                 raise error.StatusInformation(
-                    errorIndication=errind.authenticationFailure
-                )
+                    errorIndication=errind.authenticationFailure)
 
             try:
                 authHandler.authenticateIncomingMsg(
                     usmUserAuthKeyLocalized,
                     securityParameters.getComponentByPosition(4),
-                    wholeMsg
-                )
+                    wholeMsg)
 
             except error.StatusInformation:
                 usmStatsWrongDigests, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsWrongDigests')
+
                 usmStatsWrongDigests.syntax += 1
+
                 raise error.StatusInformation(
                     errorIndication=errind.authenticationFailure,
                     oid=usmStatsWrongDigests.name,
@@ -819,62 +954,81 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                 )
 
-            debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: incoming msg authenticated')
+            debug.logger & debug.FLAG_SM and debug.logger(
+                'processIncomingMsg: incoming msg authenticated')
 
             # synchronize time with authed peer
-            self.__timeline[msgAuthoritativeEngineId] = (
+            self._timeline[msgAuthoritativeEngineId] = (
                 securityParameters.getComponentByPosition(1),
                 securityParameters.getComponentByPosition(2),
                 securityParameters.getComponentByPosition(2),
                 int(time.time())
             )
 
-            timerResolution = snmpEngine.transportDispatcher is None and 1.0 or snmpEngine.transportDispatcher.getTimerResolution()
-            expireAt = int(self.__expirationTimer + 300 / timerResolution)
-            if expireAt not in self.__timelineExpQueue:
-                self.__timelineExpQueue[expireAt] = []
-            self.__timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
+            timerResolution = (snmpEngine.transportDispatcher is None and 1.0 or
+                               snmpEngine.transportDispatcher.getTimerResolution())
+
+            expireAt = int(self._expirationTimer + 300 / timerResolution)
+
+            if expireAt not in self._timelineExpQueue:
+                self._timelineExpQueue[expireAt] = []
+
+            self._timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                'processIncomingMsg: store timeline for securityEngineID %r' % (msgAuthoritativeEngineId,))
+                'processIncomingMsg: store timeline for securityEngineID '
+                '%r' % (msgAuthoritativeEngineId,))
 
         # 3.2.7
         if securityLevel == 3 or securityLevel == 2:
             if msgAuthoritativeEngineId == snmpEngineID:
                 # Authoritative SNMP engine: use local notion (SF bug #1649032)
-                (snmpEngineBoots,
-                 snmpEngineTime) = mibBuilder.importSymbols(
+                snmpEngineBoots, snmpEngineTime = mibBuilder.importSymbols(
                     '__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots', 'snmpEngineTime')
+
                 snmpEngineBoots = snmpEngineBoots.syntax
                 snmpEngineTime = snmpEngineTime.syntax.clone()
+
                 idleTime = 0
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: read snmpEngineBoots (%s), snmpEngineTime (%s) from LCD' % (
+                    'processIncomingMsg: read snmpEngineBoots (%s), '
+                    'snmpEngineTime (%s) from LCD' % (
                         snmpEngineBoots, snmpEngineTime))
+
             else:
                 # Non-authoritative SNMP engine: use cached estimates
-                if msgAuthoritativeEngineId in self.__timeline:
+                if msgAuthoritativeEngineId in self._timeline:
                     (snmpEngineBoots, snmpEngineTime,
                      latestReceivedEngineTime,
-                     latestUpdateTimestamp) = self.__timeline[
+                     latestUpdateTimestamp) = self._timeline[
                         msgAuthoritativeEngineId
                     ]
+
                     # time passed since last talk with this SNMP engine
                     idleTime = int(time.time()) - latestUpdateTimestamp
+
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        'processIncomingMsg: read timeline snmpEngineBoots %s snmpEngineTime %s for msgAuthoritativeEngineId %r, idle time %s secs' % (
-                            snmpEngineBoots, snmpEngineTime, msgAuthoritativeEngineId, idleTime))
+                        'processIncomingMsg: read timeline snmpEngineBoots %s '
+                        'snmpEngineTime %s for msgAuthoritativeEngineId %r, '
+                        'idle time %s secs' % (snmpEngineBoots, snmpEngineTime,
+                                               msgAuthoritativeEngineId,
+                                               idleTime))
                 else:
                     raise error.ProtocolError('Peer SNMP engine info missing')
 
             # 3.2.7a
             if msgAuthoritativeEngineId == snmpEngineID:
+
                 if (snmpEngineBoots == 2147483647 or
                         snmpEngineBoots != msgAuthoritativeEngineBoots or
-                        abs(idleTime + int(snmpEngineTime) - int(msgAuthoritativeEngineTime)) > 150):
+                        (abs(idleTime + int(snmpEngineTime)
+                             - int(msgAuthoritativeEngineTime))) > 150):
+
                     usmStatsNotInTimeWindows, = mibBuilder.importSymbols(
                         '__SNMP-USER-BASED-SM-MIB', 'usmStatsNotInTimeWindows')
                     usmStatsNotInTimeWindows.syntax += 1
+
                     raise error.StatusInformation(
                         errorIndication=errind.notInTimeWindow,
                         oid=usmStatsNotInTimeWindows.name,
@@ -886,6 +1040,7 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                         msgUserName=msgUserName,
                         maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                     )
+
             # 3.2.7b
             else:
                 # 3.2.7b.1
@@ -893,48 +1048,60 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                 if (msgAuthoritativeEngineBoots > snmpEngineBoots or
                         msgAuthoritativeEngineBoots == snmpEngineBoots and
                         msgAuthoritativeEngineTime > latestReceivedEngineTime):
-                    self.__timeline[msgAuthoritativeEngineId] = (
+                    self._timeline[msgAuthoritativeEngineId] = (
                         msgAuthoritativeEngineBoots,
                         msgAuthoritativeEngineTime,
                         msgAuthoritativeEngineTime,
                         int(time.time())
                     )
 
-                    timerResolution = snmpEngine.transportDispatcher is None and 1.0 or snmpEngine.transportDispatcher.getTimerResolution()
-                    expireAt = int(self.__expirationTimer + 300 / timerResolution)
-                    if expireAt not in self.__timelineExpQueue:
-                        self.__timelineExpQueue[expireAt] = []
-                    self.__timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
+                    timerResolution = (
+                            snmpEngine.transportDispatcher is None and 1.0 or
+                           snmpEngine.transportDispatcher.getTimerResolution())
+
+                    expireAt = int(self._expirationTimer + 300 / timerResolution)
+
+                    if expireAt not in self._timelineExpQueue:
+                        self._timelineExpQueue[expireAt] = []
+
+                    self._timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
 
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        'processIncomingMsg: stored timeline msgAuthoritativeEngineBoots %s msgAuthoritativeEngineTime %s for msgAuthoritativeEngineId %r' % (
-                            msgAuthoritativeEngineBoots, msgAuthoritativeEngineTime, msgAuthoritativeEngineId))
+                        'processIncomingMsg: stored timeline '
+                        'msgAuthoritativeEngineBoots %s '
+                        'msgAuthoritativeEngineTime %s for '
+                        'msgAuthoritativeEngineId '
+                        '%r' % (msgAuthoritativeEngineBoots,
+                                msgAuthoritativeEngineTime,
+                                msgAuthoritativeEngineId))
 
                 # 3.2.7b.2
                 if (snmpEngineBoots == 2147483647 or
                         msgAuthoritativeEngineBoots < snmpEngineBoots or
                         msgAuthoritativeEngineBoots == snmpEngineBoots and
-                        abs(idleTime + int(snmpEngineTime) - int(msgAuthoritativeEngineTime)) > 150):
+                        (abs(idleTime + int(snmpEngineTime)
+                             - int(msgAuthoritativeEngineTime))) > 150):
+
                     raise error.StatusInformation(
                         errorIndication=errind.notInTimeWindow,
-                        msgUserName=msgUserName
-                    )
+                        msgUserName=msgUserName)
 
         # 3.2.8a
         if securityLevel == 3:
             if usmUserPrivProtocol in self.PRIV_SERVICES:
                 privHandler = self.PRIV_SERVICES[usmUserPrivProtocol]
+
             else:
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
+
             encryptedPDU = scopedPduData.getComponentByPosition(1)
+
             if encryptedPDU is None:  # no ciphertext
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
 
             try:
                 decryptedData = privHandler.decryptData(
@@ -942,15 +1109,17 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     (securityParameters.getComponentByPosition(1),
                      securityParameters.getComponentByPosition(2),
                      securityParameters.getComponentByPosition(5)),
-                    encryptedPDU
-                )
+                    encryptedPDU)
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: PDU deciphered into %s' % debug.hexdump(decryptedData))
+                    'processIncomingMsg: PDU deciphered into '
+                    '%s' % debug.hexdump(decryptedData))
 
             except error.StatusInformation:
                 usmStatsDecryptionErrors, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsDecryptionErrors')
                 usmStatsDecryptionErrors.syntax += 1
+
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
                     oid=usmStatsDecryptionErrors.name,
@@ -962,31 +1131,32 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     msgUserName=msgUserName,
                     maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                 )
-            scopedPduSpec = scopedPduData.setComponentByPosition(0).getComponentByPosition(0)
+            scopedPduSpec = scopedPduData.setComponentByPosition(
+                0).getComponentByPosition(0)
+
             try:
                 scopedPDU, rest = decoder.decode(decryptedData, asn1Spec=scopedPduSpec)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
                     'processIncomingMsg: scopedPDU decoder failed %s' % exc)
+
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
 
             if eoo.endOfOctets.isSameTypeWith(scopedPDU):
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
+
         else:
             # 3.2.8b
             scopedPDU = scopedPduData.getComponentByPosition(0)
             if scopedPDU is None:  # no plaintext
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
 
         debug.logger & debug.FLAG_SM and debug.logger(
             'processIncomingMsg: scopedPDU decoded %s' % scopedPDU.prettyPrint())
@@ -995,7 +1165,8 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         securityName = usmUserSecurityName
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: cached msgUserName %s info by securityStateReference %s' % (
+            'processIncomingMsg: cached msgUserName %s info by '
+            'securityStateReference %s' % (
                 msgUserName, securityStateReference))
 
         # Delayed to include details
@@ -1003,6 +1174,7 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             usmStatsUnknownUserNames, = mibBuilder.importSymbols(
                 '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnknownUserNames')
             usmStatsUnknownUserNames.syntax += 1
+
             raise error.StatusInformation(
                 errorIndication=errind.unknownSecurityName,
                 oid=usmStatsUnknownUserNames.name,
@@ -1021,14 +1193,18 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         return (msgAuthoritativeEngineId, securityName, scopedPDU,
                 maxSizeResponseScopedPDU, securityStateReference)
 
-    def __expireTimelineInfo(self):
-        if self.__expirationTimer in self.__timelineExpQueue:
-            for engineIdKey in self.__timelineExpQueue[self.__expirationTimer]:
-                if engineIdKey in self.__timeline:
-                    del self.__timeline[engineIdKey]
-                    debug.logger & debug.FLAG_SM and debug.logger('__expireTimelineInfo: expiring %r' % (engineIdKey,))
-            del self.__timelineExpQueue[self.__expirationTimer]
-        self.__expirationTimer += 1
+    def _expireTimelineInfo(self):
+        if self._expirationTimer in self._timelineExpQueue:
+
+            for engineIdKey in self._timelineExpQueue[self._expirationTimer]:
+                if engineIdKey in self._timeline:
+                    del self._timeline[engineIdKey]
+                    debug.logger & debug.FLAG_SM and debug.logger(
+                        '__expireTimelineInfo: expiring %r' % (engineIdKey,))
+
+            del self._timelineExpQueue[self._expirationTimer]
+
+        self._expirationTimer += 1
 
     def receiveTimerTick(self, snmpEngine, timeNow):
-        self.__expireTimelineInfo()
+        self._expireTimelineInfo()
diff --git a/pysnmp/proto/secmod/rfc3826/priv/aes.py b/pysnmp/proto/secmod/rfc3826/priv/aes.py
index 56f69280..d000f8ed 100644
--- a/pysnmp/proto/secmod/rfc3826/priv/aes.py
+++ b/pysnmp/proto/secmod/rfc3826/priv/aes.py
@@ -38,66 +38,85 @@ class Aes(base.AbstractEncryptionService):
     local_int = random.randrange(0, 0xffffffffffffffff)
 
     # 3.1.2.1
-    def __getEncryptionKey(self, privKey, snmpEngineBoots, snmpEngineTime):
-        salt = [self.local_int >> 56 & 0xff,
-                self.local_int >> 48 & 0xff,
-                self.local_int >> 40 & 0xff,
-                self.local_int >> 32 & 0xff,
-                self.local_int >> 24 & 0xff,
-                self.local_int >> 16 & 0xff,
-                self.local_int >> 8 & 0xff,
-                self.local_int & 0xff]
+    def _getEncryptionKey(self, privKey, snmpEngineBoots, snmpEngineTime):
+        salt = [
+            self.local_int >> 56 & 0xff,
+            self.local_int >> 48 & 0xff,
+            self.local_int >> 40 & 0xff,
+            self.local_int >> 32 & 0xff,
+            self.local_int >> 24 & 0xff,
+            self.local_int >> 16 & 0xff,
+            self.local_int >> 8 & 0xff,
+            self.local_int & 0xff
+        ]
 
         if self.local_int == 0xffffffffffffffff:
             self.local_int = 0
+
         else:
             self.local_int += 1
 
-        return self.__getDecryptionKey(privKey, snmpEngineBoots, snmpEngineTime, salt) + (
-        univ.OctetString(salt).asOctets(),)
+        key, iv = self._getDecryptionKey(
+            privKey, snmpEngineBoots, snmpEngineTime, salt)
+
+        return key, iv, univ.OctetString(salt).asOctets()
+
+    def _getDecryptionKey(self, privKey, snmpEngineBoots,
+                          snmpEngineTime, salt):
 
-    def __getDecryptionKey(self, privKey, snmpEngineBoots,
-                           snmpEngineTime, salt):
         snmpEngineBoots, snmpEngineTime, salt = (
-            int(snmpEngineBoots), int(snmpEngineTime), salt
-        )
+            int(snmpEngineBoots), int(snmpEngineTime), salt)
+
+        iv = [
+            snmpEngineBoots >> 24 & 0xff,
+            snmpEngineBoots >> 16 & 0xff,
+            snmpEngineBoots >> 8 & 0xff,
+            snmpEngineBoots & 0xff,
+            snmpEngineTime >> 24 & 0xff,
+            snmpEngineTime >> 16 & 0xff,
+            snmpEngineTime >> 8 & 0xff,
+            snmpEngineTime & 0xff
+        ]
 
-        iv = [snmpEngineBoots >> 24 & 0xff,
-              snmpEngineBoots >> 16 & 0xff,
-              snmpEngineBoots >> 8 & 0xff,
-              snmpEngineBoots & 0xff,
-              snmpEngineTime >> 24 & 0xff,
-              snmpEngineTime >> 16 & 0xff,
-              snmpEngineTime >> 8 & 0xff,
-              snmpEngineTime & 0xff] + salt
+        iv += salt
 
-        return privKey[:self.KEY_SIZE].asOctets(), univ.OctetString(iv).asOctets()
+        key = privKey[:self.KEY_SIZE].asOctets()
+        iv = univ.OctetString(iv).asOctets()
+
+        return key, iv
 
     def hashPassphrase(self, authProtocol, privKey):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         return localkey.hashPassphrase(privKey, hashAlgo)
 
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
+
         return localPrivKey[:self.KEY_SIZE]
 
     # 3.2.4.1
@@ -105,21 +124,20 @@ class Aes(base.AbstractEncryptionService):
         snmpEngineBoots, snmpEngineTime, salt = privParameters
 
         # 3.3.1.1
-        aesKey, iv, salt = self.__getEncryptionKey(
-            encryptKey, snmpEngineBoots, snmpEngineTime
-        )
+        aesKey, iv, salt = self._getEncryptionKey(
+            encryptKey, snmpEngineBoots, snmpEngineTime)
 
         # 3.3.1.3
         # PyCrypto seems to require padding
-        dataToEncrypt = dataToEncrypt + univ.OctetString((0,) * (16 - len(dataToEncrypt) % 16)).asOctets()
+        padding = univ.OctetString((0,) * (16 - len(dataToEncrypt) % 16))
+        dataToEncrypt += padding
 
         try:
-            ciphertext = aes.encrypt(dataToEncrypt, aesKey, iv)
+            ciphertext = aes.encrypt(dataToEncrypt.asOctets(), aesKey, iv)
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         # 3.3.1.4
         return univ.OctetString(ciphertext), univ.OctetString(salt)
@@ -131,16 +149,15 @@ class Aes(base.AbstractEncryptionService):
         # 3.3.2.1
         if len(salt) != 8:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         # 3.3.2.3
-        aesKey, iv = self.__getDecryptionKey(
-            decryptKey, snmpEngineBoots, snmpEngineTime, salt
-        )
+        aesKey, iv = self._getDecryptionKey(
+            decryptKey, snmpEngineBoots, snmpEngineTime, salt)
 
         # PyCrypto seems to require padding
-        encryptedData = encryptedData + univ.OctetString((0,) * (16 - len(encryptedData) % 16)).asOctets()
+        padding = univ.OctetString((0,) * (16 - len(encryptedData) % 16))
+        encryptedData += padding
 
         try:
             # 3.3.2.4-6
@@ -148,5 +165,4 @@ class Aes(base.AbstractEncryptionService):
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
diff --git a/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py b/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py
index 11dd79b3..267db682 100644
--- a/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py
+++ b/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py
@@ -19,19 +19,26 @@ except ImportError:
 
     sha224 = sha256 = sha384 = sha512 = NotAvailable()
 
-from pyasn1.type import univ
 from pysnmp.proto.secmod.rfc3414.auth import base
 from pysnmp.proto.secmod.rfc3414 import localkey
 from pysnmp.proto import errind, error
 
+from pyasn1.type import univ
 
 # 7.2.4
 
 class HmacSha2(base.AbstractAuthenticationService):
-    SHA224_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 4)  # usmHMAC128SHA224AuthProtocol
-    SHA256_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 5)  # usmHMAC192SHA256AuthProtocol
-    SHA384_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 6)  # usmHMAC256SHA384AuthProtocol
-    SHA512_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 7)  # usmHMAC384SHA512AuthProtocol
+    # usmHMAC128SHA224AuthProtocol
+    SHA224_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 4)
+
+    # usmHMAC192SHA256AuthProtocol
+    SHA256_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 5)
+
+    # usmHMAC256SHA384AuthProtocol
+    SHA384_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 6)
+
+    # usmHMAC384SHA512AuthProtocol
+    SHA512_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 7)
 
     KEY_LENGTH = {
         SHA224_SERVICE_ID: 28,
@@ -59,39 +66,43 @@ class HmacSha2(base.AbstractAuthenticationService):
     
     def __init__(self, oid):
         if oid not in self.HASH_ALGORITHM:
-            raise error.ProtocolError('No SHA-2 authentication algorithm %s available' % (oid,))
-        self.__hashAlgo = self.HASH_ALGORITHM[oid]
-        self.__digestLength = self.DIGEST_LENGTH[oid]
-        self.__placeHolder = univ.OctetString((0,) * self.__digestLength).asOctets()
+            raise error.ProtocolError(
+                'No SHA-2 authentication algorithm %s available' % (oid,))
+
+        self._hashAlgo = self.HASH_ALGORITHM[oid]
+        self._digestLength = self.DIGEST_LENGTH[oid]
+        self._placeHolder = univ.OctetString(
+            (0,) * self._digestLength).asOctets()
 
     def hashPassphrase(self, authKey):
-        return localkey.hashPassphrase(authKey, self.__hashAlgo)
+        return localkey.hashPassphrase(authKey, self._hashAlgo)
 
     def localizeKey(self, authKey, snmpEngineID):
-        return localkey.localizeKey(authKey, snmpEngineID, self.__hashAlgo)
+        return localkey.localizeKey(authKey, snmpEngineID, self._hashAlgo)
 
     @property
     def digestLength(self):
-        return self.__digestLength
+        return self._digestLength
 
     # 7.3.1
     def authenticateOutgoingMsg(self, authKey, wholeMsg):
         # 7.3.1.1
-        location = wholeMsg.find(self.__placeHolder)
+        location = wholeMsg.find(self._placeHolder)
         if location == -1:
-            raise error.ProtocolError('Can\'t locate digest placeholder')
+            raise error.ProtocolError('Cannot locate digest placeholder')
+
         wholeHead = wholeMsg[:location]
-        wholeTail = wholeMsg[location + self.__digestLength:]
+        wholeTail = wholeMsg[location + self._digestLength:]
 
         # 7.3.1.2, 7.3.1.3
         try:
-            mac = hmac.new(authKey.asOctets(), wholeMsg, self.__hashAlgo)
+            mac = hmac.new(authKey.asOctets(), wholeMsg, self._hashAlgo)
 
         except errind.ErrorIndication as exc:
             raise error.StatusInformation(errorIndication=exc)
 
         # 7.3.1.4
-        mac = mac.digest()[:self.__digestLength]
+        mac = mac.digest()[:self._digestLength]
 
         # 7.3.1.5 & 6
         return wholeHead + mac + wholeTail
@@ -99,33 +110,32 @@ class HmacSha2(base.AbstractAuthenticationService):
     # 7.3.2
     def authenticateIncomingMsg(self, authKey, authParameters, wholeMsg):
         # 7.3.2.1 & 2
-        if len(authParameters) != self.__digestLength:
+        if len(authParameters) != self._digestLength:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationError
-            )
+                errorIndication=errind.authenticationError)
 
         # 7.3.2.3
         location = wholeMsg.find(authParameters.asOctets())
         if location == -1:
-            raise error.ProtocolError('Can\'t locate digest in wholeMsg')
+            raise error.ProtocolError('Cannot locate digest in wholeMsg')
+
         wholeHead = wholeMsg[:location]
-        wholeTail = wholeMsg[location + self.__digestLength:]
-        authenticatedWholeMsg = wholeHead + self.__placeHolder + wholeTail
+        wholeTail = wholeMsg[location + self._digestLength:]
+        authenticatedWholeMsg = wholeHead + self._placeHolder + wholeTail
 
         # 7.3.2.4
         try:
-            mac = hmac.new(authKey.asOctets(), authenticatedWholeMsg, self.__hashAlgo)
+            mac = hmac.new(authKey.asOctets(), authenticatedWholeMsg, self._hashAlgo)
 
         except errind.ErrorIndication as exc:
             raise error.StatusInformation(errorIndication=exc)
 
         # 7.3.2.5
-        mac = mac.digest()[:self.__digestLength]
+        mac = mac.digest()[:self._digestLength]
 
         # 7.3.2.6
         if mac != authParameters:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationFailure
-            )
+                errorIndication=errind.authenticationFailure)
 
         return authenticatedWholeMsg