Document that `os.environ` forcibly upper-cases keys on case-insensitive OSs

[brettcannon]

Documentation

os.environ docs don't mention that the keys get upper-cased automatically on e.g. Windows.

Linked PRs

• gh-101754: document that on Windows, keys in os.environ are converted to uppercase #101840
• [3.10] gh-101754: Document that Windows converts keys in os.environ to uppercase (GH-101840) #102393
• [3.11] gh-101754: Document that Windows converts keys in os.environ to uppercase (GH-101840) #102394

[brettcannon]

This came up when using Python to read the environment then trying to merge the results with Node's environment variable APIs which do not normalize.

[karrtikr]

Source code:

cpython/Lib/os.py

Line 755 in f1f3af7

return encode(key).upper()

[eryksun]

Note that it wouldn't be hard to make os.environ case insensitive but case preserving, starting with Python 3.12 or 3.13. I discussed a possible implementation in issue #73010.

[OTheDev]

Thoughts on the following (third note) suggested fix?

EDIT: on second thought, I think I prefer