gh-104922: Make PY_SSIZE_T_CLEAN not mandatory again (#105051)

Doc/c-api/arg.rst

@@ -27,9 +27,18 @@ unit; the entry in (round) parentheses is the Python object type that matches
 the format unit; and the entry in [square] brackets is the type of the C
 variable(s) whose address should be passed.
 
+.. _arg-parsing-string-and-buffers:
+
 Strings and buffers
 -------------------
 
+.. note::
+
+   On Python 3.12 and older, the macro :c:macro:`!PY_SSIZE_T_CLEAN` must be
+   defined before including :file:`Python.h` to use all ``#`` variants of
+   formats (``s#``, ``y#``, etc.) explained below.
+   This is not necessary on Python 3.13 and later.
+
 These formats allow accessing an object as a contiguous chunk of memory.
 You don't have to provide raw storage for the returned unicode or bytes
 area.
@@ -68,15 +77,6 @@ There are three ways strings and buffers can be converted to C:
    whether the input object is immutable (e.g. whether it would honor a request
    for a writable buffer, or whether another thread can mutate the data).
 
-.. note::
-
-   For all ``#`` variants of formats (``s#``, ``y#``, etc.), the macro
-   :c:macro:`PY_SSIZE_T_CLEAN` must be defined before including
-   :file:`Python.h`. On Python 3.9 and older, the type of the length argument
-   is :c:type:`Py_ssize_t` if the :c:macro:`PY_SSIZE_T_CLEAN` macro is defined,
-   or int otherwise.
-
-
 ``s`` (:class:`str`) [const char \*]
    Convert a Unicode object to a C pointer to a character string.
    A pointer to an existing string is stored in the character pointer

Doc/extending/extending.rst

@@ -70,7 +70,7 @@ the module and a copyright notice if you like).
    headers are included.
 
    It is recommended to always define ``PY_SSIZE_T_CLEAN`` before including
-   ``Python.h``.  See :ref:`parsetuple` for a description of this macro.
+   ``Python.h``.  See :ref:`arg-parsing-string-and-buffers` for a description of this macro.
 
 All user-visible symbols defined by :file:`Python.h` have a prefix of ``Py`` or
 ``PY``, except those defined in standard header files. For convenience, and
@@ -649,7 +649,7 @@ Note that any Python object references which are provided to the caller are
 
 Some example calls::
 
-   #define PY_SSIZE_T_CLEAN  /* Make "s#" use Py_ssize_t rather than int. */
+   #define PY_SSIZE_T_CLEAN
    #include <Python.h>
 
 ::
@@ -745,7 +745,7 @@ it returns false and raises an appropriate exception.
 Here is an example module which uses keywords, based on an example by Geoff
 Philbrick (philbrick@hks.com)::
 
-   #define PY_SSIZE_T_CLEAN  /* Make "s#" use Py_ssize_t rather than int. */
+   #define PY_SSIZE_T_CLEAN
    #include <Python.h>
 
    static PyObject *

Doc/whatsnew/3.13.rst

@@ -292,6 +292,13 @@ C API Changes
 New Features
 ------------
 
+* You no longer have to define the ``PY_SSIZE_T_CLEAN`` macro before including
+  :file:`Python.h` when using ``#`` formats in
+  :ref:`format codes <arg-parsing-string-and-buffers>`.
+  APIs accepting the format codes always use ``Py_ssize_t`` for ``#`` formats.
+  (Contributed by Inada Naoki in :gh:`104922`.)
+
+
 Porting to Python 3.13
 ----------------------