At the moment the default fallback class ClassDict doesn't support Python classes that have slots or use a custom setstate implementation.

I think this can be easily improved. As a suggestion I made a implementation here: https://github.com/bkats/pickle/tree/slots
I didn't yet create a pull request, since I don't know how think about this improvement. Also not sure how to get it correctly implemented in Java. (I tried something, but not sure how do instanceof check/casting correctly)

Also since I haven't Java since last century and had back then only bad experience with it. It was slow and 50% change of "hello word" already crashing with weird runtime errors. This was at Fontys (college), module Java using Visual Cafe (which is discontinued).

If your interested in the change, please let me know if I should make a pull request or maybe make some changes before hand.

I use this code (dotnet) already here: https://gitlab.com/bkats/renpygameviewer
But I did a lot more changes there, most important change for me is how "global" keyword is handled. Maybe other interesting issue?