Doc: define PY_SSIZE_T_CLEAN always (GH-12794)

Doc/c-api/intro.rst

@@ -48,7 +48,8 @@ Include Files
 All function, type and macro definitions needed to use the Python/C API are
 included in your code by the following line::
 
-   #include "Python.h"
+   #define PY_SSIZE_T_CLEAN
+   #include <Python.h>
 
 This implies inclusion of the following standard headers: ``<stdio.h>``,
 ``<string.h>``, ``<errno.h>``, ``<limits.h>``, ``<assert.h>`` and ``<stdlib.h>``
@@ -60,6 +61,9 @@ This implies inclusion of the following standard headers: ``<stdio.h>``,
    headers on some systems, you *must* include :file:`Python.h` before any standard
    headers are included.
 
+   It is recommended to always define ``PY_SSIZE_T_CLEAN`` before including
+   ``Python.h``.  See :ref:`arg-parsing` for a description of this macro.
+
 All user visible names defined by Python.h (except those defined by the included
 standard headers) have one of the prefixes ``Py`` or ``_Py``.  Names beginning
 with ``_Py`` are for internal use by the Python implementation and should not be

Doc/extending/embedding.rst

@@ -53,6 +53,7 @@ interface. This interface is intended to execute a Python script without needing
 to interact with the application directly. This can for example be used to
 perform some operation on a file. ::
 
+   #define PY_SSIZE_T_CLEAN
    #include <Python.h>
 
    int

Doc/extending/extending.rst

@@ -55,8 +55,9 @@ called ``spam``, the C file containing its implementation is called
 :file:`spammodule.c`; if the module name is very long, like ``spammify``, the
 module name can be just :file:`spammify.c`.)
 
-The first line of our file can be::
+The first two lines of our file can be::
 
+   #define PY_SSIZE_T_CLEAN
    #include <Python.h>
 
 which pulls in the Python API (you can add a comment describing the purpose of
@@ -68,6 +69,9 @@ the module and a copyright notice if you like).
    headers on some systems, you *must* include :file:`Python.h` before any standard
    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.
+
 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
 since they are used extensively by the Python interpreter, ``"Python.h"``
@@ -729,7 +733,8 @@ 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)::
 
-   #include "Python.h"
+   #define PY_SSIZE_T_CLEAN  /* Make "s#" use Py_ssize_t rather than int. */
+   #include <Python.h>
 
    static PyObject *
    keywdarg_parrot(PyObject *self, PyObject *args, PyObject *keywds)
@@ -1228,7 +1233,7 @@ The function :c:func:`spam_system` is modified in a trivial way::
 
 In the beginning of the module, right after the line ::
 
-   #include "Python.h"
+   #include <Python.h>
 
 two more lines must be added::
 

Doc/faq/extending.rst

@@ -280,6 +280,7 @@ solution then is to call :c:func:`PyParser_ParseString` and test for ``e.error``
 equal to ``E_EOF``, which means the input is incomplete.  Here's a sample code
 fragment, untested, inspired by code from Alex Farber::
 
+   #define PY_SSIZE_T_CLEAN
    #include <Python.h>
    #include <node.h>
    #include <errcode.h>
@@ -318,6 +319,7 @@ complete example using the GNU readline library (you may want to ignore
    #include <stdio.h>
    #include <readline.h>
 
+   #define PY_SSIZE_T_CLEAN
    #include <Python.h>
    #include <object.h>
    #include <compile.h>

Doc/includes/custom.c

+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 
 typedef struct {

Doc/includes/custom2.c

+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "structmember.h"
 

Doc/includes/custom3.c

+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "structmember.h"
 

Doc/includes/custom4.c

+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "structmember.h"
 

Doc/includes/run-func.c

+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 
 int

Doc/includes/sublist.c

+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 
 typedef struct {