How do you determine if an IP address is private, in Python?

Check out the IPy module. If has a function iptype() that seems to do what you want:

>>> from IPy import IP
>>> ip = IP('127.0.0.0/30')
>>> ip.iptype()
'PRIVATE'

Since Python 3.3 there is an ipaddress module in the stdlib that you can use.

>>> import ipaddress
>>> ipaddress.ip_address('192.168.0.1').is_private
True

If using Python 2.6 or higher I would strongly recommend to use a backport of this module.