One way of monkeypatch is using Set class defined in stubout module of pymox package.
https://code.google.com/p/pymox/source/browse/trunk/stubout.py#108
monkeyPatch(module, 'myFunc', lambda n: someObject)
monkeypatch is only recommendable while unit testing the code if no other approach works to avoid it.
using monkeypatch in runtime to change the behaviour of class without affecting the class defination can be hazardous.