There is no usage of _PySys_GetObjectId / _PySys_GetObjectId private APIs in CPython project.
Since these APIs use _Py_Identifier as the parameter, it looks good to be removed this time when there is no usage at all.
But before removing these APIs, I will investigate the current usage of external projects even if they are not intended to be used from outside.

./top_5000/datatable-1.0.0.tar.gz: datatable-1.0.0/src/core/python/obj.cc: _PySys_GetObjectId(&PyId_stdin)  // borrowed ref
./top_5000/datatable-1.0.0.tar.gz: datatable-1.0.0/src/core/python/obj.cc: _PySys_GetObjectId(&PyId_stdout)  // borrowed ref
./top_5000/datatable-1.0.0.tar.gz: datatable-1.0.0/src/core/python/obj.cc: _PySys_GetObjectId(&PyId_stderr)  // borrowed ref
./top_5000/pickle5-0.0.12.tar.gz: pickle5-0.0.12/pickle5/_pickle.c: modules = _PySys_GetObjectId(&PyId_modules);

@pitrou

https://github.com/pitrou/pickle5-backport/blob/e6117502435aba2901585cc6c692fb9582545f08/pickle5/_pickle.c#L1937

Do you have a plan to use PySys_GetObject("modules") instead of _PySys_GetObjectId(&PyId_modules)?

@vstinner
From my view, PySys_GetObject is available since Python3.2 both APIs look safe to remove.

https://pypi.org/project/pickle5/ should not be used on Python 3.8 and newer: it's a backport for Python 3.7 and older.

> From my view, PySys_GetObject is available since Python3.2 both APIs look safe to remove.

_PySys_GetObjectId() and _PySys_GetObjectId() are private API and can be removed anytime. We don't provide any backward compatibility warranty on the private API:
https://docs.python.org/dev/c-api/stable.html#c-api-stability

"Names prefixed by an underscore, such as _Py_InternalState, are private API that can change without notice even in patch releases."

> ./top_5000/datatable-1.0.0.tar.gz: datatable-1.0.0/src/core/python/obj.cc: _PySys_GetObjectId(&PyId_stdout)  // borrowed ref

It would be nice to notify datatable, or even propose a PR, if the _PySys_GetObjectId() is removed in Python 3.11.

> ./top_5000/datatable-1.0.0.tar.gz: datatable-1.0.0/src/core/python/obj.cc: _PySys_GetObjectId(&PyId_stdin)  // borrowed ref

All three occurences look like this [1] for two years (see git blame):

    #ifndef Py_LIMITED_API
      _PySys_GetObjectId(&PyId_stdin)  // borrowed ref
    #else
      PySys_GetObject("stdin")         // borrowed ref
    #endif

So everything is fixed already.

[1]: https://github.com/h2oai/datatable/search?q=_PySys_GetObjectId

New changeset bb1c543f4a183f5cfdf15aad59f59094d50b37fd by Dong-hee Na in branch 'main':
bpo-46987: Remove _PySys_GetObjectId / _PySys_GetObjectId (GH-31835)
https://github.com/python/cpython/commit/bb1c543f4a183f5cfdf15aad59f59094d50b37fd