I am a bit curious if PyDict and PySet can have RwLock<Dict<T>> instead of this InnerDict structure

I agree, for separation of concerns Dict seems like it would work best as a standard-ish data structure that requires a mutable reference to mutate.

I have a actually started that way but it became very complex. One of my goals is to not hold the lock while "python" code is running. In the Dict lookup we call __eq__ so we need to release that lock but in order to do that from PyDict and PySet we will need to split the implementation of Dict to smaller methods that do not call "python" code.
Do you guys think this is the way to go? That will make a lot of code duplication in PyDict and PySet.

Hmm, that is tricky. I don't really think I have a preference either way for mutable/interior mutable Dict.

I will push this as other object are dependent on PyDictRef. We can always change the implementation in the future.