C API: Add PyType_GetModuleByDef() to the limited C API version 3.13

[vstinner]

I propose adding PyType_GetModuleByDef() to the limited C API version 3.13. The function was added to Python 3.9, the function is now well tested. We could add it way earlier to the limited C API.

cc @encukou

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The PyType_GetModuleByDef() function is needed to access the module state in C function which don't get a module as first parameter, but only an instance of a heap type. Heap types should be created with PyType_FromModuleAndSpec(module, spec, bases) to store the module in the type. PyType_GetModuleByDef(type) gives the module and then PyModule_GetState() gives the moulde state.

Examples of functions which don't get a module argument:

• Class methods
• Most slots, examples: tp_new, tp_richcompare, tp_iternext, etc.
• PyGetSetDef getter and setter functions

Without PyType_GetModuleByDef(), many static types cannot be converted to heap types.

The following stdlib extensions use PyType_GetModuleByDef()

Modules/_asynciomodule.c
Modules/_bz2module.c
Modules/_collectionsmodule.c
Modules/_csv.c
Modules/_decimal/_decimal.c
Modules/_elementtree.c
Modules/_functoolsmodule.c
Modules/_io/_iomodule.h
Modules/_pickle.c
Modules/_queuemodule.c
Modules/_randommodule.c
Modules/_sqlite/module.h
Modules/_ssl.c
Modules/_ssl.h
Modules/_struct.c
Modules/_testmultiphase.c
Modules/_threadmodule.c
Modules/_xxinterpchannelsmodule.c
Modules/_zoneinfo.c
Modules/arraymodule.c
Modules/cjkcodecs/multibytecodec.c
Modules/clinic/_testmultiphase.c.h
Modules/itertoolsmodule.c
Modules/socketmodule.c
Python/Python-tokenize.c

Linked PRs

• gh-116937

[vstinner]

Attached PR gh-116937 implements the change.

[vstinner]

The function was added by issue gh-90771.

[encukou]

I agree. It can be implemented using only limited API, but the CPython implementation can pull tricks that make it worth calling as a function.

I'll be interested in what other members of the C-API WG have to say.

[vstinner]

It can be implemented using only limited API

I don't think that it's possible in practice. For example, Python 3.13 adds BEGIN_TYPE_LOCK() with _PyCriticalSection which is not part of the stable ABI.

[encukou]

AFAIK, that's for the freethreading experiment. I hope that when the experiment is done, it won't require adding non-limited calls to stable ABI extensions.

[vstinner]

@encukou:

I'll be interested in what other members of the C-API WG have to say.

Ok, I created issue https://github.com/capi-workgroup/decisions/issues/20.

[vstinner]

Ok, I created issue https://github.com/capi-workgroup/decisions/issues/20.

The C API Working Group approved this addition: https://github.com/capi-workgroup/decisions/issues/20.

[vstinner]

Implemented in change https://github.com/python/cpython/commit/507896d97dcff2d7999efa264b29d9003c525c49