How to convert from hex-encoded string to a "human readable" string?

Posted by John Jensen on Stack Overflow See other posts from Stack Overflow or by John Jensen
Published on 2013-07-01T22:53:38Z Indexed on 2013/07/01 23:05 UTC
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Filed under:

python-2.7

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hex

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net-snmp

I'm using the Net-SNMP bindings for python and I'm attempting to grab an ARP cache from a Brocade switch. Here's what my code looks like:

#!/usr/bin/env python

import netsnmp

def get_arp():
    oid = netsnmp.VarList(netsnmp.Varbind('ipNetToMediaPhysAddress'))
    res = netsnmp.snmpwalk(oid, Version=2, DestHost='10.0.1.243', Community='public')
    return res

arp_table = get_arp()

print arp_table

The SNMP code itself is working fine. Output from snmpwalk looks like this:

<snip>
IP-MIB::ipNetToMediaPhysAddress.128.10.200.6.158 = STRING: 0:1b:ed:a3:ec:c1
IP-MIB::ipNetToMediaPhysAddress.129.10.200.6.162 = STRING: 0:1b:ed:a4:ac:c1
IP-MIB::ipNetToMediaPhysAddress.130.10.200.6.166 = STRING: 0:1b:ed:38:24:1
IP-MIB::ipNetToMediaPhysAddress.131.10.200.6.170 = STRING: 74:8e:f8:62:84:1
</snip>

But my output from the python script yields a tuple of hex-encoded strings that looks like this:

('\x00$8C\x98\xc1', '\x00\x1b\xed;_A', '\x00\x1b\xed\xb4\x8f\x81', '\x00$86\x15\x81', '\x00$8C\x98\x81', '\x00\x1b\xed\x9f\xadA', ...etc)

I've spent some time googling and came across the struct module and the .decode("hex") string method, but the .decode("hex") method doesn't seem to work:

Python 2.7.3 (default, Apr 10 2013, 06:20:15)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> hexstring = '\x00$8C\x98\xc1'
>>> newstring = hexstring.decode("hex")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/encodings/hex_codec.py", line 42, in hex_decode
    output = binascii.a2b_hex(input)
TypeError: Non-hexadecimal digit found
>>>

And the documentation for struct is a bit over my head.

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