error with netsnmp.snmpwalk in libsnmp-python

Here's the python code:

import netsnmp
oid = netsnmp.Varbind('sysDescr')
result = netsnmp.snmpwalk(oid, Version = 2, DestHost="localhost", Community="public")

and, here's the output
[L:root@net-monitor] /opt/ip-mgmt# python test.py
error: walk: unknown python error (varlist)#

also,

[L:root@net-monitor] /opt/ip-mgmt# python
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import netsnmp
>>> oid = netsnmp.Varbind('sysDescr')
>>> result = netsnmp.snmpwalk(oid, Version = 2, DestHost="localhost", Community="public")
error: walk: unknown python error (varlist)>>>
TypeError: expected string or Unicode object, NoneType found

(I pressed enter and TypeError line occured)

and,

[L:root@net-monitor] /opt/ip-mgmt# snmpwalk -v2c -c public localhost sysDescr
SNMPv2-MIB::sysDescr.0 = STRING: Linux net-monitor 2.6.32-37-server #81-Ubuntu SMP Fri Dec 2 20:49:12 UTC 2011 x86_64

So SNMP works.

System: Lucid amd64, with the most current packages.