[Python-checkins] gh-101754: Document that Windows converts keys in `os.environ` to uppercase (GH-101840)

[zooba]

https://github.com/python/cpython/commit/4e7c0cbf59595714848cf9827f6e5b40c3985924
commit: 4e7c0cbf59595714848cf9827f6e5b40c3985924
branch: main
author: Owain Davies <116417456+OTheDev at users.noreply.github.com>
committer: zooba <steve.dower at microsoft.com>
date: 2023-03-03T10:51:32Z
summary:

gh-101754: Document that Windows converts keys in `os.environ` to uppercase (GH-101840)

files:
M Doc/library/os.rst

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 85924d0e4836..23ce98785bed 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -201,6 +201,11 @@ process and user.
    ``'surrogateescape'`` error handler. Use :data:`environb` if you would like
    to use a different encoding.
 
+   On Windows, the keys are converted to uppercase. This also applies when
+   getting, setting, or deleting an item. For example,
+   ``environ['monty'] = 'python'`` maps the key ``'MONTY'`` to the value
+   ``'python'``.
+
    .. note::
 
       Calling :func:`putenv` directly does not change :data:`os.environ`, so it's better