Okay, dirty little secret, PyProtocols uses metaclasses in a really extreme way. I assumed they would, and in looking, yes they do. There's rather a lack of real code being demo'd though. For instance, what does a "normal" class + interface declaration look like? Hard to tell, as the test cases are quite round-about in getting defined (looks like they were heavily refactored a few times) and the reference documentation seems to be missing all of the actual functionality of the system.