Remove broken PySequence_Fast() function from the limited C API

[vstinner]

The limited C API has the function PySequence_Fast() which should be used with these macros:

• PySequence_Fast_GET_SIZE()
• PySequence_Fast_GET_ITEM()
• PySequence_Fast_ITEMS()

Problem: none of these 3 macros work with the limited C API. The whole PySequence_Fast() API is broken in the limited C API.

Example:

#define PySequence_Fast_GET_ITEM(o, i)\
     (PyList_Check(o) ? PyList_GET_ITEM((o), (i)) : PyTuple_GET_ITEM((o), (i)))

PyList_GET_ITEM() and PyTuple_GET_ITEM() are not part of the limited C API, so PySequence_Fast_GET_ITEM() cannot be used in the limited C API.

I propose to remove PySequence_Fast() and these 3 macros from the limited C API, since they are incompatible and never worked with the limited C API.

• Issue
• Pull request

Vote:

• @encukou
• @erlend-aasland
• @mdboom
• @serhiy-storchaka
• @vstinner
• @zooba

[serhiy-storchaka]

I support this. It is clear to me that they were not excluded from the limited C API due to oversight.

PySequence_ITEM also slipped in the limited C API. It was excluded in issue python/cpython#77919 (PR python/cpython#7477).

[encukou]

+1 for removing the macros; yes, they never worked in limited API (and since PEP 652 they were never “officially” part of limited API); moving them to Include/cpython is the right thing to do.

The PySequence_Fast function itself works. Third-party code can, theoretically, require a result of PySequence_Fast as input.
If y'all think it should go I won't block the removal, but I think it's unnecessary. As minor, benign mistake of the past, it doesn't need fixing.

[vstinner]

Ping @erlend-aasland.

[vstinner]

Thanks for voting. I close the issue.

@encukou:

Third-party code can, theoretically, require a result of PySequence_Fast as input.
If y'all think it should go I won't block the removal, but I think it's unnecessary.

At least, the function remains available in the stable ABI.