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GeezerVison is showing github.com — gh-160427: Return None from TextIOWrapper.buffer when detached by cmaloney · Pull Request #160802 · python/cpython

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@cmaloney

@cmaloney cmaloney commented Oct 28, 2026 •
edited by bedevere-app Bot
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gh-154523 turned the buffer member descriptor into a getter that raises ValueError when the buffer is NULL, and the backport shipped in 3.14.9 and 3.15.1. That changed the behavior of hasattr(stream, "buffer") to raise after .detach(). Restore the old member descriptor result (None) while keeping the critical section for free-threaded safety.

  • Issue: hasattr(stream, "buffer") fails with ValueError if buffer is detached #160427

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@cmaloney
pythongh-160427: Return None from TextIOWrapper.buffer when detached
58f2c10 
pythongh-154523 turned the buffer member descriptor into a getter that raises
ValueError when the buffer is NULL, and the backport shipped in 3.14.9
and 3.15.1. That made hasattr(stream, "buffer") raise after detach().
Restore the old member descriptor result (None) while keeping the
critical section.
@cmaloney cmaloney added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 28, 2026
@bedevere-app bedevere-app Bot added the awaiting review label Oct 28, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 28, 2026
hasattr(stream, "buffer") fails with ValueError if buffer is detached #160427
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@cmaloney cmaloney linked an issue Oct 28, 2026 that may be closed by this pull request
hasattr(stream, "buffer") fails with ValueError if buffer is detached #160427
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@cmaloney

cmaloney commented Oct 28, 2026

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cc: @kumaraditya303 , @vstinner : This attribute changed from returning None when unset to raising a ValueError. That was backported to stable branches breaking backwards compatibility.
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@cmaloney
cmaloney merged commit 3422197 into python:main Nov 5, 2026
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@bedevere-app bedevere-app Bot removed the awaiting review label Nov 5, 2026
@miss-islington-app

miss-islington-app Bot commented Nov 5, 2026

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Thanks @cmaloney for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖
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@cmaloney
cmaloney deleted the gh-160427-textio-buffer-none branch November 5, 2026 21:40
@miss-islington-app

miss-islington-app Bot commented Nov 5, 2026

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Sorry, @cmaloney, I could not cleanly backport this to 3.14 due to a conflict.

Please backport manually with cherry_picker, see the devguide for more information.

cherry_picker 3422197f5481ac1b3134e2633332415a02959ba4 3.14
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@miss-islington-app miss-islington-app Bot assigned cmaloney Nov 5, 2026
@bedevere-app

bedevere-app Bot commented Nov 5, 2026

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GH-161449 is a backport of this pull request to the 3.15 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Nov 5, 2026
@bedevere-app

bedevere-app Bot commented Nov 5, 2026

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GH-161450 is a backport of this pull request to the 3.14 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Nov 5, 2026
cmaloney added a commit that referenced this pull request Nov 5, 2026
@miss-islington @cmaloney
[3.15] gh-160427: Return None from TextIOWrapper.buffer when detached (…
4af98bd 
…GH-160802) (#161449)

gh-154523 turned the buffer member descriptor into a getter that raises
ValueError when the buffer is NULL, and the backport shipped in 3.14.9
and 3.15.1. That made hasattr(stream, "buffer") raise after detach().
Restore the old member descriptor result (None) while keeping the
critical section.
(cherry picked from commit 3422197)

Co-authored-by: Cody Maloney <[email protected]>
cmaloney added a commit that referenced this pull request Nov 5, 2026
@cmaloney
[3.14] gh-160427: Return None from TextIOWrapper.buffer when detached (…
9106913 
…GH-160802) (#161450)

gh-154523 turned the buffer member descriptor into a getter that raises
ValueError when the buffer is NULL, and the backport shipped in 3.14.9
and 3.15.1. That made hasattr(stream, "buffer") raise after detach().
Restore the old member descriptor result (None) while keeping the
critical section.
(cherry picked from commit 3422197)
vstinner
vstinner approved these changes Nov 6, 2026
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@vstinner vstinner left a comment

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Post-merge review.

Ooops, it's not good to change io module behavior in bugfix releases. Well, it happens, it should now be fixed as any other bug/regression. At least, we do now have a test checking for the expected behavior.

LGTM. _io_TextIOWrapper_buffer_get_impl() code is safe on Free Threading since it uses a critical section.

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@vstinner vstinner vstinner approved these changes

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hasattr(stream, "buffer") fails with ValueError if buffer is detached

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@cmaloney @vstinner
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