ObjectIdentity class additionally supports just a MIB module name

initializer in which case if resolves into either first or last symbol
in given MIB. Another new option is just a MIB symbol initializer without
specifying MIB module.

4 files changed, 73 insertions, 18 deletions

diff --git a/CHANGES b/CHANGES
index 0fcf308..6187887 100644
--- a/CHANGES
+++ b/CHANGES
@@ -93,7 +93,11 @@ Revision 4.2.6
 - The oneliner's MibVariable MIB lookup subsystem redesigned for more
   generality to mimic OBJECT-TYPE macro capabilities related to SNMP
   PDU handling. The two new classed are ObjectIdentity and ObjectType.
-  This new subsystem is moved from a scope of oneliner to more common
+  The ObjectIdentity class additionally supports just a MIB module name
+  initializer in which case if resolves into either first or last symbol
+  in given MIB. Another option is just a MIB symbol initializer without 
+  specifying MIB module.
+  This new subsystem is moved from the scope of oneliner to more common
   pysnmp.smi.rfc1903 scope to more naturally invoke it from whatever
   part of pysnmp requires MIB services.
 - MibBuilder now prepends the contents of environment variables it 
diff --git a/TODO b/TODO
index d1f36b9..23393a8 100644
--- a/TODO
+++ b/TODO
@@ -49,3 +49,6 @@ Sparse notes on major existing problems/plans
 * Implement TCP transport support
 
 * Rework UNIX sockets transport to make it STREAM-type.
+
+* The get-first/get-last operations of pysnmp.smi.rfc1902.ObjectIdentity()
+  may need a means to deal only with specific node types.
diff --git a/examples/smi/mib-lookup.py b/examples/smi/mib-lookup.py
index 1c83afa..a208897 100644
--- a/examples/smi/mib-lookup.py
+++ b/examples/smi/mib-lookup.py
@@ -32,6 +32,36 @@ mibVar = rfc1902.ObjectIdentity(str(mibVar)).resolveWithMib(mibView)
 
 print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
 
+# Obtain MIB object information by a mix of OID/label parts
+mibVar = rfc1902.ObjectIdentity((1,3,6,1,2,'mib-2',1,'sysDescr')).resolveWithMib(mibView)
+
+print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
+
+# Obtain MIB object information by a label
+mibVar = rfc1902.ObjectIdentity('iso.org.dod.internet.mgmt.mib-2.system.sysDescr').resolveWithMib(mibView)
+
+print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
+
+# Obtain the first MIB object in given MIB module
+mibVar = rfc1902.ObjectIdentity('SNMPv2-MIB').resolveWithMib(mibView)
+
+print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
+
+# Obtain the last MIB object in given MIB module
+mibVar = rfc1902.ObjectIdentity('SNMPv2-MIB', last=True).resolveWithMib(mibView)
+
+print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
+
+# Another way to obtain the first (or last) symbol in MIB module
+mibVar = rfc1902.ObjectIdentity('SNMPv2-MIB', '').resolveWithMib(mibView)
+
+print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
+
+# Obtain MIB symbol from whatever MIB it is defined at (MIB should be loaded)
+mibVar = rfc1902.ObjectIdentity('', 'sysDescr', 0).resolveWithMib(mibView)
+
+print(mibVar.prettyPrint(), tuple(mibVar), str(mibVar))
+
 # Create an OID-value pair (called variable-binding in SNMP)
 varBind = rfc1902.ObjectType(
     rfc1902.ObjectIdentity('SNMPv2-MIB', 'sysObjectID', 0), '1.3.6.1'
diff --git a/pysnmp/smi/rfc1902.py b/pysnmp/smi/rfc1902.py
index 8e5f905..4c23c31 100644
--- a/pysnmp/smi/rfc1902.py
+++ b/pysnmp/smi/rfc1902.py
@@ -113,19 +113,31 @@ class ObjectIdentity:
 
         self.__indices = ()
 
-        if len(self.__args) == 1:  # OID or label
+        if len(self.__args) == 1:  # OID or label or MIB module
             debug.logger & debug.flagMIB and debug.logger('resolving %s as OID or label' % self.__args)
             try:
-                self.__oid = rfc1902.ObjectName(self.__args[0])
+                # pyasn1 ObjectIdentifier or sequence of ints or string OID
+                self.__oid = rfc1902.ObjectName(self.__args[0])  # OID
             except PyAsn1Error:
-                try:
-                    label = tuple(self.__args[0].split('.'))
-                except ValueError:
-                    raise SmiError('Bad OID format %r' % (self.__args[0],))
-                prefix, label, suffix = mibViewController.getNodeNameByOid(
-                    label
-                )
-             
+                # sequence of sub-OIDs and labels
+                if isinstance(self.__args[0], (list, tuple)):
+                    prefix, label, suffix = mibViewController.getNodeName(
+                        self.__args[0]
+                    )
+                # string label
+                elif '.' in self.__args[0]:
+                    prefix, label, suffix = mibViewController.getNodeNameByOid(
+                        tuple(self.__args[0].split('.'))
+                    )
+                # MIB module name
+                else:
+                    modName = self.__args[0]
+                    mibViewController.mibBuilder.loadModules(modName)
+                    if self.__kwargs.get('last'):
+                        prefix, label, suffix = mibViewController.getLastNodeName(modName)
+                    else:
+                        prefix, label, suffix = mibViewController.getFirstNodeName(modName)
+
                 if suffix:
                     try:
                         suffix = tuple([ int(x) for x in suffix ])
@@ -175,16 +187,22 @@ class ObjectIdentity:
 
             return self
         elif len(self.__args) > 1:  # MIB, symbol[, index, index ...]
-            self.__modName = self.__args[0]
-            if self.__args[1]:
+            # MIB, symbol, index, index
+            if self.__args[0] and self.__args[1]:
+                self.__modName = self.__args[0]
                 self.__symName = self.__args[1]
-            else:
-                mibViewController.mibBuilder.loadModules(self.__modName)
+            # MIB, ''
+            elif self.__args[0]:
+                mibViewController.mibBuilder.loadModules(self.__args[0])
                 if self.__kwargs.get('last'):
-                    oid,_,_ = mibViewController.getLastNodeName(self.__modName)
+                    prefix, label, suffix = mibViewController.getLastNodeName(self.__args[0])
                 else:
-                    oid,_,_ = mibViewController.getFirstNodeName(self.__modName)
-                _, self.__symName, _ = mibViewController.getNodeLocation(oid)
+                    prefix, label, suffix = mibViewController.getFirstNodeName(self.__args[0])
+                self.__modName, self.__symName, _ = mibViewController.getNodeLocation(prefix)
+            # '', symbol, index, index
+            else:
+                prefix, label, suffix = mibViewController.getNodeName(self.__args[1:])
+                self.__modName, self.__symName, _ = mibViewController.getNodeLocation(prefix)
 
             mibNode, = mibViewController.mibBuilder.importSymbols(
                 self.__modName, self.__symName