I've been working on lancelot: a specification and verification library for python, inspired by the particular idiom of test driven development that goes under the banner of BDD. (And the word idiom is a film reference: Sir Lancelot: "Um, I think when I'm in this idiom, I sometimes get a bit, uh, sort of carried away.")
The code is available in a launchpad bazaar repository at http://launchpad.net/lancelot, and the packages can be downloaded from the Cheese Shop at http://pypi.python.org/pypi/lancelot. Versions for both Python 3.x and 2.5 are available: if you check them out please let me know what you think!
PS: Although I'm aware of PySpec and SpeciPy, I haven't actually used them, so I can't really compare lancelot with what they offer. My motivation for starting a new project was that I wanted something to use with Python 3, and I thought I could put my long experience with TDD to good use. (Perhaps I should qualify "long experience"... I've been using JUnit since 2000, was a committer on the Java XmlUnit project, and in 2003-4 I had the pleasure of working alongside Steve Purcell, the author of the Python unittest package, and Nat Pryce, Steve Freeman and Joe Walnes, the authors of the JMock framework. More recently, after some discussion with Andrew Glover, I have been experimenting with easyb, the Java/Groovy BDD framework).