C API: Add PyWeakref_GetRef() function

[vstinner]

PyWeakref_GET_OBJECT() and PyWeakref_GetObject() return a borrowed reference to the object, or a borrowed reference to None if the object has been finalized. This API is error-prone and not easy to use.

This API was discussed in 2016: https://mail.python.org/archives/list/python-dev@python.org/thread/6BIPI4MCMAZFLJNIZB4JLTBW2COCACQQ/

I propose adding a new PyWeakref_GetRef() C API function which returns a new strong reference to the object, or NULL if the object has been finalized.

Linked PRs

• gh-105927: Refactor weakrefobject.c #105928
• gh-105927: Add _PyWeakref_GET_REF() internal function #105929
• gh-105927: Add PyWeakref_GetRef() function #105932
• gh-105927: _abc and _thread use PyWeakref_GetRef() #105961
• gh-105927: type_from_ref() uses _PyWeakref_GET_REF() #105963
• gh-105927: _ctypes use PyWeakref_GetRef() #105964
• gh-105927: _ssl uses _PyWeakref_GET_REF() #105965
• gh-105927: Fix test_weakref_capi() refleak #105966
• gh-105927: finalize_modules_clear_weaklist() uses _PyWeakref_GET_REF() #105971
• gh-105927: Add _PyWeakref_IS_DEAD() function #105992
• gh-105927: Avoid calling PyWeakref_GET_OBJECT() #105997
• gh-105927: PyImport_AddModule() uses _PyWeakref_GET_REF() #106001
• gh-105927: _ssl GET_SOCKET() uses _PyWeakref_GET_REF() #106002
• gh-105927: Deprecate PyWeakref_GetObject() function #106006
• gh-105927: Remove _PyWeakref_GetWeakrefCount() #106007
• gh-105927: PyWeakref_GetRef() returns 1 on success #106561
• gh-105927: Limit PyWeakref_GetRef() to limited C API 3.13 #117091

[erlend-aasland]

[...] or NULL if the object has been finalized.

With an error set? If no, would you need to call PyErr_Occurred() to find out if an error has occurred? See also capi-workgroup/problems#1

[vstinner]

With an error set? If no, would you need to call PyErr_Occurred() to find out if an error has occurred? See also capi-workgroup/problems#1

No error is set. See PR #105929 for the first part of the implementation.