Bug report

Bug description:

Starting with Python 3.12 if a file is in PATH that does not end with PATHEXT, but happens to be named the same as the searched command it is returned instead of the real command later in PATH which includes PATHEXT.

# Assume:
# PATH=C:\foo;C:\WINDOWS\system32
# "C:\foo\cmd" exists
# "C:\WINDOWS\system32\cmd.exe" exists

import shutil
print(shutil.which('cmd'))
# Actual: C:\foo\cmd
# Expected: C:\WINDOWS\system32\cmd.exe (3.11 result)

I have verified that this change was introduced with #103179 and reverting it fixes the issue.

@csm10495 ^

Downstream context: mesonbuild/meson#13886

CPython versions tested on:

3.12

Operating systems tested on:

Windows

Linked PRs

• gh-127001: Fix PATHEXT issues in shutil.which() on Windows #127035
• [3.13] gh-127001: Fix PATHEXT issues in shutil.which() on Windows (GH-127035) #127156
• [3.12] gh-127001: Fix PATHEXT issues in shutil.which() on Windows (GH-127035) #127158