[C API] Add PyImport_ImportModuleAttr(mod_name, attr_name) helper function

[vstinner]

Feature or enhancement

Proposal:

Python has an internal _PyImport_GetModuleAttrString(mod_name, attr_name) helper function to import a module and get a module attribute. I propose to make this function public to be able to use it outside Python.

UPDATE: Function renamed to PyImport_ImportModuleAttrString().

The function is convenient to use and is used by the following files in Python:

• Modules/arraymodule.c
• Modules/cjkcodecs/cjkcodecs.h
• Modules/_ctypes/callbacks.c
• Modules/_datetimemodule.c
• Modules/_decimal/_decimal.c
• Modules/_elementtree.c
• Modules/faulthandler.c
• Modules/_lsprof.c
• Modules/_operator.c
• Modules/_pickle.c
• Modules/posixmodule.c
• Modules/selectmodule.c
• Modules/_sqlite/connection.c
• Modules/_sqlite/module.c
• Modules/_sre/sre.c
• Modules/timemodule.c
• Modules/_zoneinfo.c
• Objects/abstract.c
• Objects/fileobject.c
• Objects/memoryobject.c
• Parser/pegen.c
• Parser/tokenizer/file_tokenizer.c
• Python/import.c
• Python/pylifecycle.c

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-128911: Add PyImport_ImportModuleAttr() function #128912
• gh-128911: Add tests on the PyImport C API #128915
• [3.13] gh-128911: Add tests on the PyImport C API (#128915) #128960
• [3.12] gh-128911: Add tests on the PyImport C API (GH-128915) (GH-128960) #128989

[encukou]

IMO, the *String functions should generally have variants that take PyObject*.
So, if we add this we should also add PyImport_GetModuleAttr.

[vstinner]

So, if we add this we should also add PyImport_GetModuleAttr.

Ok, I added PyImport_GetModuleAttr() to my PR.

[malemburg]

This sounds like a useful addition. The fact that the internal API is already used a lot in CPython is evidence enough 😄

And BTW: I like that you're starting to approach C API design from the perspective of a C programmer again.

Rich C APIs make it a joy programming against them, while minimalist APIs only result in others creating additional layers on top, which adds fragmentation, overall increased maintenance and loss of design control. 👍

[vstinner]

See also #129367 which proposes adding PySys_GetAttr().