the most recent version of PySNMP (like 4.1.x) has SNMP v3 support. (not sure if its 100% or not...check with developer).
Anyhow I think the documentation explains how to use PySNMP (http://pysnmp.sourceforge.net/docs/4.1.x/index.html) ....i think the "interface" is common amongst the different SNMP versions that are supported by PySNMP. So i think if you use the CommandGenerator.nextCmd method...its the same format for snmp v2 and v3, etc. It took me a little bit to grasp the API but once I did it works well (although I am not using SNMP v3) -- http://mail.python.org/mailman/listinfo/python-list