objectIdentity object not properly initialized

[CharlesJu1]

I installed pysnmp and tried examples from the website snmplabs.com. I got the following error:

cju@ubuntu-16:~$ python3
Python 3.5.2 (default, Nov 12 2018, 13:43:14) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
>>> 
>>> from pysnmp.hlapi import *
>>> x = ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0)
>>> 
>>> tuple(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/cju/.local/lib/python3.5/site-packages/pysnmp/smi/rfc1902.py", line 606, in __len__
    raise SmiError('%s object not properly initialized' % self.__class__.__name__)
pysnmp.smi.error.SmiError: ObjectIdentity object not properly initialized

However, I could run the following example code ok.

>>> errorIndication, errorStatus, errorIndex, varBinds = next(
...     getCmd(SnmpEngine(),
...            CommunityData('public', mpModel=0),
...            UdpTransportTarget(('demo.snmplabs.com', 161)),
...            ContextData(),
...            ObjectType(ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0)))
... )
>>> 
>>> if errorIndication:
...     print(errorIndication)
... elif errorStatus:
...     print('%s at %s' % (errorStatus.prettyPrint(),
...                         errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
... else:
...     for varBind in varBinds:
...         print(' = '.join([x.prettyPrint() for x in varBind]))
... 
SNMPv2-MIB::sysDescr.0 = Linux zeus 4.8.6.5-smp #2 SMP Sun Nov 13 14:58:11 CDT 2016 i686

[etingof]

That's right, ObjectIdentity works lazily. If you want it to get resolved against a MIB you need to explicitly call .resolveWithMib() as noted in the docs.

You will also need the MibViewController object, just follow this example - the first three lines of that script seem to do what you are trying to do.

[CharlesJu1]

Thanks etingof. It works following your reply. I now understand that pysnmp needs mibs to be installed as a python module named like mibname.py. Is there a command to install some other mibs besides the built-in mibs installed along with pysnmp? How to list what mibs are already installed?

[etingof]

No need to compile MIB files into Python. If you configure the source of ASN.1 MIBs, the translation would happen behind the scene.

But you can also compile ASN.1 MIB(s) into Python with mibdump tool.

[CharlesJu1]

If I configure the source of ASN.1 MIBs, it will download and translate the ASN.1 MIB on the fly. That may take some more time than a local copy of MIB. I noticed that SNMPv2-MIB.py exists both in ~/.pysnmp/mibs and ~/.local/lib/python3.5/site-packages/pysnmp/smi/mibs. However, IF-MIB.py only exists in ~/.pysnmp/mibs folder. Why is that?

[etingof]

If I configure the source of ASN.1 MIBs, it will download and translate the ASN.1 MIB on the fly. That may take some more time than a local copy of MIB.

This downloading and translation happens just once and results in caching the translated module in ~/.pysnmp/mibs/. Once cached files are there, no more translation should occur.

I noticed that SNMPv2-MIB.py exists both in ~/.pysnmp/mibs and ~/.local/lib/python3.5/site-packages/pysnmp/smi/mibs. However, IF-MIB.py only exists in ~/.pysnmp/mibs folder. Why is that?

I am guessing that you played with MIB compiler at the moment when pysnmp was not available so the compiler tried to translate SNMPv2-MIB.py. Normally, you should use SNMPv2-MIB.py shipped with pysnmp because this is one of the core MIBs that are not fully translatable because they require some custom code on top of automatically generated code.

[CharlesJu1]

Thanks etingof. When using mibdump.py to generate MIBs in pysnmp format, can I generate mib indices? Where is the indices file and how it is used?

[frsoto]

MibViewController

Hi.
the link no longer exists
I have the same doubt

Regards..

[lextm]

@frsoto You can read #429 for more details. The domain snmplabs.com was lost so any connection to it today is risky.