CODEWITHSUNDEEP
python-2.7hexnet-snmp
John Jensen
John Jensen

Reputation: 422

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

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.

Upvotes: 1

Views: 8040

Answers (2)

FlavorScape
FlavorScape

Reputation: 14269

Change "hex" to "hex_codec" for Python < 3

This applies to python 3+ Possible to use?

>>> codecs.decode(b"4f6c6567", "hex_codec")
b'Oleg'
>>> codecs.getdecoder("hex_codec")(b"4f6c6567")
(b'Oleg', 8)

Upvotes: 1

John Jensen
John Jensen

Reputation: 422

Some more clever google-fu uncovered this code snippet, which gives me the results I expect:

def convertMac(octet):
    mac = [binascii.b2a_hex(x) for x in list(octet)]
    return ":".join(mac)

So "decoding" is really a misnomer, because this code also yields a proper result (with encode and decode appearing to be syntactic sugar for binascii.a2b() and binascii.b2a()):

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.
>>> string = '\x00$8\xa1\x1c2'
>>> string.encode("hex")
'002438a11c32'
>>>

Upvotes: 2

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