What are the state of the art python frameworks/libs to learn code from?

Reading well designed and well written code is an excellent way of learning from the best programmers out there.

I am looking for a recommendation of some python codebase that is:

• written in pythonic idiomatic way
• not too cryptic / hacky
• not too domain specific
• not over-engineered

The standard library is obviously a good example, but can you recommend some other packages? I am sure there is a lot of projects in PyPI worth the time. Any suggestions?