Recently I had to work with some Python code which needs to be compatible with both the hopefully-soon-to-be-finally-deprecated Python 2.7 and recent 3.x versions.

String handling can be a tricky issue, particularly if the string in question needs to be cast to a Unicode object. Take the following example:

#!/usr/bin/env python

import ipaddress

addresses = list(ipaddress.ip_network(unicode('192.168.1.0/24')));

for address in addresses:
    print(address)

This does of course fail in Python 3.x with an error like:

Traceback (most recent call last):
  File "./python.py", line 5, in 
    addresses = list(ipaddress.ip_network(unicode('192.168.1.0/24')));
NameError: name 'unicode' is not defined

Remove the unicode() wrapper and it fails in Python 2.x with:

ipaddress.AddressValueError: '192.168.1.0/24' does not appear to be an IPv4 or IPv6 network. Did you pass in a bytes (str in Python 2) instead of a unicode object?

The solution is to use the "six" compatibility layer and add the following directive, which reassigns unicode() to a mutually compatible function:

#!/usr/bin/env python

import ipaddress

from six import u as unicode

addresses = list(ipaddress.ip_network(unicode('192.168.1.0/24')));

for address in addresses:
    print(address)

Note that the "six" compatibility layer may need to be installed separately, in RedHat et al via the packages python2x-six and python3x-six respectively.

Useful links

• Six: Python 2 and 3 Compatibility Library
• Building a Python 2/3 compatible Unicode Sandwich
• Strings, Bytes, and Unicode in Python 2 and 3