Reformat `isAccessAllowed()` for clarity

1 files changed, 30 insertions, 13 deletions

diff --git a/pysnmp/proto/acmod/rfc3415.py b/pysnmp/proto/acmod/rfc3415.py
index 1e14ab34..3c5afe9e 100644
--- a/pysnmp/proto/acmod/rfc3415.py
+++ b/pysnmp/proto/acmod/rfc3415.py
@@ -8,14 +8,14 @@ from pysnmp.smi.error import NoSuchInstanceError
 from pysnmp.proto import errind, error
 from pysnmp import debug
 
-__powOfTwoSeq = [128, 64, 32, 16, 8, 4, 2, 1]
-
 
 # 3.2
 class Vacm(object):
     """View-based Access Control Model"""
     accessModelID = 3
 
+    _powOfTwoSeq = (128, 64, 32, 16, 8, 4, 2, 1)
+
     def isAccessAllowed(self,
                         snmpEngine,
                         securityModel,
@@ -31,25 +31,30 @@ class Vacm(object):
                 securityModel, securityName, securityLevel, viewType, contextName, variableName))
 
         # 3.2.1
-        vacmContextEntry, = mibInstrumController.mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
+        vacmContextEntry, = mibInstrumController.mibBuilder.importSymbols(
+            'SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
+
         tblIdx = vacmContextEntry.getInstIdFromIndices(contextName)
         try:
-            vacmContextName = vacmContextEntry.getNode(
+            vacmContextEntry.getNode(
                 vacmContextEntry.name + (1,) + tblIdx
             ).syntax
+
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noSuchContext)
 
         # 3.2.2
-        vacmSecurityToGroupEntry, = mibInstrumController.mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB',
-                                                                                  'vacmSecurityToGroupEntry')
+        vacmSecurityToGroupEntry, = mibInstrumController.mibBuilder.importSymbols(
+            'SNMP-VIEW-BASED-ACM-MIB', 'vacmSecurityToGroupEntry')
         tblIdx = vacmSecurityToGroupEntry.getInstIdFromIndices(
             securityModel, securityName
         )
+
         try:
             vacmGroupName = vacmSecurityToGroupEntry.getNode(
                 vacmSecurityToGroupEntry.name + (3,) + tblIdx
             ).syntax
+
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noGroupName)
 
@@ -57,6 +62,7 @@ class Vacm(object):
         vacmAccessEntry, = mibInstrumController.mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry'
         )
+
         # XXX partial context name match
         tblIdx = vacmAccessEntry.getInstIdFromIndices(
             vacmGroupName, contextName, securityModel, securityLevel
@@ -74,51 +80,62 @@ class Vacm(object):
 
         try:
             viewName = vacmAccessEntry.getNode(entryIdx).syntax
+
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noAccessEntry)
-        if not len(viewName):
+
+        if not viewName:
             raise error.StatusInformation(errorIndication=errind.noSuchView)
 
         # XXX split onto object & instance ?
 
         # 3.2.5a
-        vacmViewTreeFamilyEntry, = mibInstrumController.mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB',
-                                                                                 'vacmViewTreeFamilyEntry')
+        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 1:
+
+        while True:
             vacmViewTreeFamilySubtree = vacmViewTreeFamilyEntry.getNextNode(
                 treeName
             )
             vacmViewTreeFamilyMask = vacmViewTreeFamilyEntry.getNextNode(
                 maskName
             )
+
             treeName = vacmViewTreeFamilySubtree.name
             maskName = vacmViewTreeFamilyMask.name
+
             if initialTreeName != treeName[:len(initialTreeName)]:
                 # 3.2.5b
                 raise error.StatusInformation(errorIndication=errind.notInView)
+
             l = len(vacmViewTreeFamilySubtree.syntax)
             if l > len(variableName):
                 continue
+
             if vacmViewTreeFamilyMask.syntax:
                 mask = []
                 for c in vacmViewTreeFamilyMask.syntax.asNumbers():
-                    mask = mask + [b & c for b in __powOfTwoSeq]
+                    mask.extend([b & c for b in self._powOfTwoSeq])
+
                 m = len(mask) - 1
                 idx = l - 1
                 while idx:
-                    if idx > m or mask[idx] and \
-                            vacmViewTreeFamilySubtree.syntax[idx] != variableName[idx]:
+                    if (idx > m or mask[idx] and
+                            vacmViewTreeFamilySubtree.syntax[idx] != variableName[idx]):
                         break
                     idx -= 1
+
                 if idx:
                     continue  # no match
+
             else:  # no mask
                 if vacmViewTreeFamilySubtree.syntax != variableName[:l]:
                     continue  # no match
+
             # 3.2.5c
             return error.StatusInformation(errorIndication=errind.accessAllowed)