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GeezerVison is showing github.com — gh-140774: Fix clearing the read-only file attribute on Windows by yhay81 · Pull Request #154852 · python/cpython

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@yhay81

@yhay81 yhay81 commented Jul 29, 2026 •
edited by bedevere-app Bot
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Fixes #140774.

On Windows, SetFileInformationByHandle() leaves attributes unchanged when FILE_BASIC_INFO.FileAttributes is zero. Thus clearing the sole read-only attribute silently failed through os.chmod(..., follow_symlinks=True), os.fchmod(), and pathlib.Path.chmod(). Use FILE_ATTRIBUTE_NORMAL in that case.

Regression tests cover both handle-based paths. test_os and test_pathlib pass.

(AI-assisted; reproduced and verified locally on Windows 11.)

  • Issue: Path.chmod() silently fails on Windows when archive bit is cleared and follow_symlinks=True #140774

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@yhay81
pythongh-140774: Fix clearing the read-only file attribute on Windows
c5f2eb0 
SetFileInformationByHandle() interprets a FILE_BASIC_INFO with
FileAttributes == 0 as "leave the attributes unchanged", so clearing
the read-only flag of a file with no other attribute set was silently
ignored by os.chmod(follow_symlinks=True), os.fchmod() and
pathlib.Path.chmod().  Substitute FILE_ATTRIBUTE_NORMAL in that case.

Co-Authored-By: Claude Fable 5 <[email protected]>
@bedevere-app bedevere-app Bot added the awaiting review label Jul 29, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Jul 29, 2026
Path.chmod() silently fails on Windows when archive bit is cleared and follow_symlinks=True #140774
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github-actions Bot commented Oct 29, 2026

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This PR is stale because it has been open for 90 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label Oct 29, 2026
yhay81 added 2 commits November 12, 2026 09:25
@yhay81
Merge remote-tracking branch 'upstream/main' into pythongh-140774-hch…
3b50d3d 
…mod-clear-readonly
@yhay81
pythongh-140774: Set SetFileAttributesW argtypes and cover fd/Path.chmod
80c74d0
@yhay81

yhay81 commented Nov 12, 2026

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Merged latest main to refresh CI and expanded Win32ChmodTests to explicitly type SetFileAttributesW and cover os.chmod(fd, ...) and Path.chmod() as well.

cc @serhiy-storchaka @zooba (as author/reviewer of win32_hchmod() in GH-113049 / GH-113192) whenever you have a chance to take a look — check_chmod in test_posix didn't hit this because newly created NTFS files have FILE_ATTRIBUTE_ARCHIVE set, so info.FileAttributes only becomes 0 (which SetFileInformationByHandle / FILE_BASIC_INFO treats as "leave unchanged") when READONLY was the sole attribute.
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serhiy-storchaka
serhiy-storchaka approved these changes Nov 12, 2026
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@serhiy-storchaka serhiy-storchaka left a comment

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Thank you for your report and fix. The tests look excessive for such simple fix, but I do not see a way to make them simpler.

LGTM. 👍

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Comment thread Lib/test/test_os/test_windows.py Outdated
finally:
os.close(fd)

def test_pathlib_chmod_clears_readonly_without_other_attributes(self):

@serhiy-storchaka serhiy-storchaka Nov 12, 2026

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This test is redundant. Path.chmod() uses os.chmod().

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@yhay81 yhay81 Nov 12, 2026

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Good point — removed in 362a02a. Thank you for the review!

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting review labels Nov 12, 2026
@serhiy-storchaka serhiy-storchaka added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes and removed stale Stale PR or inactive for long period of time. labels Nov 12, 2026
@yhay81
pythongh-140774: Remove redundant Path.chmod() test from Win32ChmodTests
362a02a
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Path.chmod() silently fails on Windows when archive bit is cleared and follow_symlinks=True

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@yhay81 @serhiy-storchaka
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