bpo-36588: On AIX, remove major version from sys.platform (GH-12787)

On AIX, sys.platform doesn't contain the major version anymore.
Always return 'aix', instead of 'aix3' .. 'aix7'.  Since
older Python versions include the version number, it is recommended to
always use sys.platform.startswith('aix').

Doc/library/sys.rst

@@ -1014,7 +1014,7 @@ always available.
    This string contains a platform identifier that can be used to append
    platform-specific components to :data:`sys.path`, for instance.
 
-   For Unix systems, except on Linux, this is the lowercased OS name as
+   For Unix systems, except on Linux and AIX, this is the lowercased OS name as
    returned by ``uname -s`` with the first part of the version as returned by
    ``uname -r`` appended, e.g. ``'sunos5'`` or ``'freebsd8'``, *at the time
    when Python was built*.  Unless you want to test for a specific system
@@ -1024,12 +1024,15 @@ always available.
           # FreeBSD-specific code here...
       elif sys.platform.startswith('linux'):
           # Linux-specific code here...
+      elif sys.platform.startswith('aix'):
+          # AIX-specific code here...
 
    For other systems, the values are:
 
    ================ ===========================
    System           ``platform`` value
    ================ ===========================
+   AIX              ``'aix'``
    Linux            ``'linux'``
    Windows          ``'win32'``
    Windows/Cygwin   ``'cygwin'``
@@ -1042,6 +1045,12 @@ always available.
       older Python versions include the version number, it is recommended to
       always use the ``startswith`` idiom presented above.
 
+   .. versionchanged:: 3.8
+      On AIX, :attr:`sys.platform` doesn't contain the major version anymore.
+      It is always ``'aix'``, instead of ``'aix5'`` or ``'aix7'``.  Since
+      older Python versions include the version number, it is recommended to
+      always use the ``startswith`` idiom presented above.
+
    .. seealso::
 
       :attr:`os.name` has a coarser granularity.  :func:`os.uname` gives

Doc/whatsnew/3.8.rst

@@ -700,6 +700,11 @@ Changes in Python behavior
   raised when getting the attribute from the type dictionary are no longer
   ignored.  (Contributed by Serhiy Storchaka in :issue:`35459`.)
 
+* On AIX, :attr:`sys.platform` doesn't contain the major version anymore.
+  It is always ``'aix'``, instead of ``'aix3'`` .. ``'aix7'``.  Since
+  older Python versions include the version number, it is recommended to
+  always use the ``sys.platform.startswith('aix')``.
+  (Contributed by M. Felt in :issue:`36588`.)
 
 Changes in the Python API
 -------------------------

Misc/NEWS.d/next/Core and Builtins/2019-04-11-14-36-55.bpo-36588.wejLoC.rst

@@ -0,0 +1,5 @@
+On AIX, :attr:`sys.platform` doesn't contain the major version anymore.
+Always return ``'aix'``, instead of ``'aix3'`` .. ``'aix7'``.  Since
+older Python versions include the version number, it is recommended to
+always use ``sys.platform.startswith('aix')``.
+Contributed by M. Felt.

configure

@@ -3281,6 +3281,7 @@ then
     MACHDEP="$ac_md_system$ac_md_release"
 
     case $MACHDEP in
+	aix*) MACHDEP="aix";;
 	linux*) MACHDEP="linux";;
 	cygwin*) MACHDEP="cygwin";;
 	darwin*) MACHDEP="darwin";;
@@ -10199,7 +10200,6 @@ fi
 
 
 
-
 if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
 	if test -n "$ac_tool_prefix"; then
   # Extract the first word of "${ac_tool_prefix}pkg-config", so it can be a program name with args.

configure.ac

@@ -404,6 +404,7 @@ then
     MACHDEP="$ac_md_system$ac_md_release"
 
     case $MACHDEP in
+	aix*) MACHDEP="aix";;
 	linux*) MACHDEP="linux";;
 	cygwin*) MACHDEP="cygwin";;
 	darwin*) MACHDEP="darwin";;