Compile with STABLE_ABI for Python 3.13 and later

[hpkfft]

How does specifying the following for scikit-build-core in pyproject.toml:

[tool.scikit-build]
wheel.py-api = "cp313"

interact with specifying STABLE_ABI to nanobind_add_module()?
I think the latter sets Py_LIMITED_API=0x030C0000.

How best to define Py_LIMITED_API=0x030D0000 and build using the stable ABI when the extension is intended only to support Python 3.13 and later?

I don't actually want to do this for any extensions I have written; I just thought I'd share this scenario for future consideration.

[wjakob]

nanobind doesn't have any benefits building for Python 3.13 or later. So if your goal is to make stable ABI builds, I would set this to 3.12.

[wjakob]

Does this answer your question/can I close this discussion?

[hpkfft]

Well, if #854 is merged into master, then there is a benefit to defining Py_LIMITED_API=0x030D0000.
As I wrote above, I don't need this myself, but it might be useful to others.
Also, I hope one day that free threading will be usable from stable ABI builds.
So, I think it's worth leaving this open as an "Ideas" discussion.

[wjakob]

Ah, I missed that. Sorry, but would it be possible to stick with 3.12 API?

I put quite a bit of effort into adding stuff to CPython to make the 3.12 stable ABI a really good compilation target. All of nanobind is designed to harmonize with that.

[hpkfft]

I think it's reasonable for nanobind to stay with the 3.12 stable ABI. The complex type caster is not a compelling reason to revisit that decision. (For those interested in implementation details of the complex type caster, I'll add some comments to #854)