[brightsize]

Have you had a look at Coconut? I don't know if it'll push all your buttons but whenever I hear someone who's reasonably content with Python but wants more FP goodies I always think of it. https://github.com/evhub/coconut . It's basically a superset of Python3 that transpiles into Python3 and is compatible with MyPy. I don't think I'd code Python w/o it ever again assuming I had the choice. The biggest negative for me is that there's no IDE support for the language last I looked, though of course you can work with the transpiler output (plain Python) in your favorite Python IDE. It might be fun to play around with, I know that I really enjoyed it but then I got spoiled by the language+tooling of Scala3, but if you don't have that option ...

[chubot]

I actually want the imperative Python style, but with sum types. So it's more like "Rust with GC" I suppose.

I used to write in a functional style, and then I wrote Python for decades, and my brain flipped. Now I like imperative code :) I guess it's all the usual things about liking break / continue / early return, local mutation, flat code rather than nested code, etc.