There is a new tools called Lettuce that promises to be a Pythonic version of Cucumber. It is starting with Django integration. That plus the existing testing tools in Django make it pretty good for unit testing.
There's also a tool called Windmill that provides a solid browser-based testing tool for building GUI tests. Couple that with a tool like Lettuce for writing acceptance tests and the straight unittest and nosetests and I'd say you're set.
The thing to remember, there's a slightly different culture between Ruby and Python. Ruby has a preference for tests above all else. In Python it's documentation. As such, there's not a million and one testing frameworks in Python, just a few really solid ones with the occasional outlier (like Lettuce).
Hope this helps.