Description

JelleZijlstra

opened on Oct 29, 2026

Issue body actions

fnmatch.filter contains a check:

    if os.path is posixpath:
        # normcase on posix is NOP. Optimize it away from the loop.

It calls normcase on the paths to be filtered only on non-Posix platforms.

The check dates from 2001 and the comment was probably true then. But nowadays, os.path.normcase does do something even on Posix: it normalizes path-like objects into strs or bytes.

So on MacOS I get:

>>> import fnmatch
>>> from pathlib import Path
>>> fnmatch.filter([Path("hi")], "hi")
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    fnmatch.filter([Path("hi")], "hi")
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/Users/jelle/py/cpython/Lib/fnmatch.py", line 61, in filter
    if match(name):
       ~~~~~^^^^^^
TypeError: expected string or bytes-like object, got 'PosixPath'

But this will work on Windows.

I think this is should be fixed for two reasons:

• It's an unnecessary difference in behavior between platforms. Python should work the same across OSes as much as possible, and there's no good reason for the behavior to differ here.
• In general, we want path-related functions to accept path-like objects (PEP 519)

However, we've generally treated PEP 519 changes as new features, so let's change this on main only.

Discovered in python/typeshed#16647

Linked PRs

• gh-160900: support path-like objects in fnmatch filters #160980

Activity

1. JelleZijlstra

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-featureA feature request or enhancementA feature request or enhancement

   and removed

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Oct 29, 2026
2. picnixz commented on Oct 29, 2026

   

   picnixz

   on Oct 29, 2026

   Member

   More actions

   Yeah, this is somethign I found when I implemented filterfalse but I was afraid to change the implementation. I don't think we need this small optimization anymore.
3. zedzhen commented on Oct 29, 2026

   

   zedzhen

   on Oct 29, 2026

   More actions

   fnmatch.fnmatch normalizes both parameters (this is explicitly stated in the documentation), and the documentation says

   fnmatch.filter is the same as [n for n in names if fnmatch(n, pat)], but implemented more efficiently.
4. MonikaDvorackova

   added 5 commits that reference this issue on Oct 30, 2026

   pythongh-160900: add NEWS entry

   feb3718

   pythongh-160900: document path-like support and test mixed filename t…

   e32415c

   pythongh-160900: support path-like objects in fnmatch filters

   ab8c256

   pythongh-160900: normalize path-like names in filterfalse

   6fe66e6

   pythongh-160900: Remove redundant fspath calls

   584ec30

Issue actions