I disagree. Twisted is a sprawling codebase, it started as a game library that turned into an async library along the way, you need to read books to get the full documentation, and some of it doesn't even have docstrings or comments.
You are right it is not the best example of an open source project, and for what you say it neither is a good python project example. But is there any other place you can get the hold of working async with python, it may be hard, but you would learn a lot.
But maybe there are other async python projects that I don't know of. If you know of any please post them, I would also like to learn more about the subject.