http://cheeseshop.python.org/pypi/partial/1.0

A partial class is a fragment of a class definition;
partial classes allow to spread the definition of
a class over several modules. One location serves
as the original definition of the class.

To extend a class original_module.FullClass with
an additional function, one writes

from partial import *
import original_module

class ExtendedClass(partial, original_module.FullClass):
     def additional_method(self, args):
         body
     more_methods

This module is licensed under the Academic Free License v3.0.