PEP 803: Stable ABI for Free-Threaded Builds

[encukou (Petr Viktorin)]

@pf_moore

That seems to contradict the term “stable”, or at least the expectations people have of that term, though…?

Yes. But for free-threading, the stable ABI needs to be broken in some way.

@philthompson

The bit I’m struggling with is understanding whether or not existing
cp39-abi3 (for example) wheels will be supported by Python v3.15???

Yes, but only in the regular (non-free-threaded) builds of 3.15+.

@philthompson

Things would be easier (but not impossible) if that ABI
supported the existing ABI for a couple of years or so.

It should be possible to make a single ABI compatible with 3.11+ (non-free-threaded) and 3.15+ (all builds).^[1] Personally, I’d be happy to do it – please convince the SC that it’s a good idea! Currently it seems the complexity in testing and supporting this is not worth it.
It could be done as an “add-on” to PEP 803 – basically, extending the compatibility to lower versions.

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1. ① Add Py_OPAQUE_OBJECT as a user-settable knob for limited API 3.14 and below; ② add a shim for PEP 793’s PyModExport (ugly but self-contained); ③ add a few shims for things that only became non-static functions in or 3.15; ④ add a abi3t wheel tag, rather than relying on cp315-abi3 ↩︎