From 4e7c0cbf59595714848cf9827f6e5b40c3985924 Mon Sep 17 00:00:00 2001
From: Owain Davies <116417456+OTheDev@users.noreply.github.com>
Date: Fri, 3 Mar 2023 17:51:32 +0700
Subject: [PATCH] gh-101754: Document that Windows converts keys in
 `os.environ` to uppercase (GH-101840)

---
 Doc/library/os.rst | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 85924d0e483..23ce98785be 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