[Python-checkins] bpo-26329: update os.path.normpath documentation (GH-20138) (GH-27094)

[ambv]

https://github.com/python/cpython/commit/443db64f496d3988d20cfda2c3c2ceb6702df36f
commit: 443db64f496d3988d20cfda2c3c2ceb6702df36f
branch: 3.10
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2021-07-12T17:07:46+02:00
summary:

bpo-26329: update os.path.normpath documentation (GH-20138) (GH-27094)

(cherry picked from commit 66c5853406bbcccecf35372795078c0641a5f385)

Co-authored-by: Furkan Onder <furkanonder at protonmail.com>

files:
M Doc/library/os.path.rst
M Lib/posixpath.py

diff --git a/Doc/library/os.path.rst b/Doc/library/os.path.rst
index d06d9ce8c9e3d..e2f43424df15e 100644
--- a/Doc/library/os.path.rst
+++ b/Doc/library/os.path.rst
@@ -340,6 +340,14 @@ the :mod:`glob` module.)
    that contains symbolic links.  On Windows, it converts forward slashes to
    backward slashes. To normalize case, use :func:`normcase`.
 
+  .. note::
+      On POSIX systems, in accordance with `IEEE Std 1003.1 2013 Edition; 4.13
+      Pathname Resolution <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>`_,
+      if a pathname begins with exactly two slashes, the first component
+      following the leading characters may be interpreted in an implementation-defined
+      manner, although more than two leading characters shall be treated as a
+      single character.
+
    .. versionchanged:: 3.6
       Accepts a :term:`path-like object`.
 
diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 259baa64b193b..195374613a779 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -352,6 +352,7 @@ def normpath(path):
     initial_slashes = path.startswith(sep)
     # POSIX allows one or two initial slashes, but treats three or more
     # as single slash.
+    # (see http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13)
     if (initial_slashes and
         path.startswith(sep*2) and not path.startswith(sep*3)):
         initial_slashes = 2