Make PY_SSIZE_T_CLEAN not mandatory again

[methane]

Feature or enhancement

Use ssize_t version API regardless PY_SSIZE_T_CLEAN is defined.

No change to ABI.

Pitch

After Python 3.12 become EOL, extension developers can forget about PY_SSIZE_T_CLEAN completely.

Previous discussion

https://mail.python.org/archives/list/python-dev@python.org/thread/KSREO43D6GQWO5LMVIU2LF7CP4IBYT2C/#FG44N6RL5CT5O3XQ6UV6LBLUCET7IF6I

Linked PRs

• gh-104922: Make PY_SSIZE_T_CLEAN not mandatory #104923
• gh-104922: Make PY_SSIZE_T_CLEAN not mandatory again #105051
• gh-104922: Doc: extending: add note about PY_SSIZE_T_CLEAN #106314
• gh-104922: remove PY_SSIZE_T_CLEAN #106315

[vstinner]

After Python 3.12 become EOL, extension developers can forget about PY_SSIZE_T_CLEAN completely.

Python stdlib extensions still define the PY_SSIZE_T_CLEAN macro. Is it still useful? It's unclear to me.

Also, the official documentation also requires to define the PY_SSIZE_T_CLEAN macro: https://docs.python.org/dev/extending/extending.html

The first two lines of our file can be:

#define PY_SSIZE_T_CLEAN
#include <Python.h>

(...)

It is recommended to always define PY_SSIZE_T_CLEAN before including Python.h.

[methane]

See right after the doc. I added the link to https://docs.python.org/dev/c-api/arg.html#arg-parsing-string-and-buffers

And there is a note about it at link target.

Note On Python 3.12 and older, the macro PY_SSIZE_T_CLEAN must be defined before including Python.h to use all # variants of formats (s#, y#, etc.) explained below. This is not necessary on Python 3.13 and later.

I didn't remove the recommendation because user may want to support older Pythons.

Python stdlib extensions still define the PY_SSIZE_T_CLEAN macro. Is it still useful? It's unclear to me.

I didn't remove them to ease review and avoid conflicts. But I will remove them all.

[vstinner]

The (extension) doc should just explain that the macro was needed on Python 3.12 and older.