The following PEP 573 were not added to the Windows list of stable ABI symbols (PC/python3dll.c):
- PyModule_AddType
- PyType_FromModuleAndSpec
- PyType_GetModule
- PyType_GetModuleState

I'd like to add them.

Also, the PEP introduces the (METH_FASTCALL | METH_KEYWORDS | METH_METHOD) calling convention, but METH_FASTCALL is not part of the stable ABI (and it other uses are not suitable for stable ABI).
I propose adding a new value, METH_METHOD_ARGS_KWD (name up for bikeshedding), which would be equal to (METH_FASTCALL | METH_KEYWORDS | METH_METHOD) but part of the limited API.

Does that sound like a good idea?


On the sprint, Steve mentioned that it would be possible to backport this to Python 3.9.1, even though it would mean a weird minor-version requirement.
I no longer think that's a good idea: fixing the stable ABI will be a longer-term project, and I don't want to fight issues in a 3.9 backport.

FWIW, for the longer-term project, I started a brainstorming repo at https://github.com/encukou/abi3 (Yes, it has some overlap with Victor's more general notes at https://pythoncapi.readthedocs.io/ )
But I'd like to get the additions above in to unblock #42111 before I start on improving the stable ABI in general.