Update: We have developed our own test doubles framework. It is open source. Please check it out at www.pyDoubles.org
Mocker and PyMox are two isolation frameworks, or test doubles frameworks able to create mocks and stubs. Mocker is not being released frequently but contains pretty much all the features one need to test-drive. On the other hand PyMox is being developed but it's got an ugly Java-like syntax with does not look like Python. I don't say that Java syntax is ugly, in fact, I like it. What I say is that Python's got its own conventions (PEP-8) and PyMox does not respect it.
Which one to use? I think I need the two of them. PyMox is terrible for stubbing out functions. Awful API for stubs and more than that, it didn't work for me sometimes. However, it's great for mocks. Mocker is nice for stubs and powerful although the proxy/patch stuff is weird. I use both, Mocker for stubs and PyMox for mocks 🙂