Woah! Okay, that's very cool. I thought it was much more limited than that (for the stable abi). Awesome!
It seems like they use mostly normal python as a bridge with the rust codebase. So from what I've seen on their repo, they mostly do not use any CPython APIs (a part from a few wrappers I think). Which makes sense!
That makes sense: I would assume polars mostly converts from Python to rust at the edge then it works in rust internally.
Though I’ve not really looked at the details I’d assume most of the missing stuff would be “intimate” APIs of builtin types. And all the macros leveraging implementation details.
See https://pypi.org/project/polars/1.9.0/#files cp38-abi3 wheels means they are compatible with cpython 3.8 or later.