fnmatch.filter and glob don't match uppercase names under Windows simulation

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@sricharanreddycheruku is already working on this.

Since Oct 7, 2026.

  • #1352 by @sricharanreddycheruku — open

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
68/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
python
Domain
operating-systems, testing

Research direction

Start with the reproduced calls to fnmatch.filter, glob.glob, and the pyfakefs Patcher configured with OSType.WINDOWS. Compare their matching and directory-listing paths with fnmatch.fnmatch, then run the supplied reproduction to verify behavior. Done means uppercase names match case-insensitively for both filter and glob under Windows simulation without changing the already-correct single-name result.

Written by the indexing model from the issue text.

Description

Describe the bug
With Windows simulated on a POSIX host, fnmatch.filter doesn't match names containing uppercase letters, even when the pattern is in the same case. glob.glob misses the same files. fnmatch.fnmatch on a single name gives the right answer.

Expected: matching is case-insensitive, as on Windows.

fnmatch.fnmatch('B.TXT', '*.txt')       -> True   (correct)
fnmatch.filter(['B.TXT'], '*.txt')      -> []     (expected ['B.TXT'])
fnmatch.filter(['B.TXT'], '*.TXT')      -> []     (expected ['B.TXT'])
glob.glob('*.txt', root_dir='C:\\d')    -> []     (expected ['B.TXT'])

I see the same results running from a case-sensitive and from a case-insensitive APFS volume.

How To Reproduce
Run on a POSIX host:

import fnmatch, glob, os
from pyfakefs.fake_filesystem import OSType
from pyfakefs.fake_filesystem_unittest import Patcher

with Patcher() as p:
    p.fs.os = OSType.WINDOWS
    os.makedirs('C:\\d')
    open('C:\\d\\B.TXT', 'w').close()
    print(fnmatch.fnmatch('B.TXT', '*.txt'))
    print(fnmatch.filter(['B.TXT'], '*.txt'))
    print(fnmatch.filter(['B.TXT'], '*.TXT'))
    print(glob.glob('*.txt', root_dir='C:\\d'))

Your environment

macOS-27.0-arm64-arm-64bit-Mach-O
Python 3.14.7 (main, Aug  5 2026, 10:29:49) [Clang 21.0.0 (clang-2100.1.1.101)]
pyfakefs 6.2.0
ModuleNotFoundError: No module named 'pytest'
Dominant language
Python
Stars
756
Forks
111
Avg merge
3d 21h
Merged PRs (30d)
10

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