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GeezerVison is showing github.com — gh-159739: Keep text I/O state valid across reentrant callbacks by jelle-openai · Pull Request #160398 · python/cpython

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@jelle-openai

@jelle-openai jelle-openai commented Oct 22, 2026 •
edited by bedevere-app Bot
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A raw read can reinitialize a TextIOWrapper as write-only, and codec callbacks or finalizers can release an encoder, decoder, or decoded chunk while a read or write still needs it. This can crash the interpreter. Check that a decoder is still available after reading, keep codecs alive across calls, and read the chunk length before transferring ownership. Also recheck StringIO after converting the truncate size because index() can close the stream.

  • Issue: Fix minor safety issues #159739

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@jelle-openai
pythongh-159739: Keep text I/O state valid across reentrant callbacks
024accb 
A raw read can reinitialize a TextIOWrapper as write-only, and codec callbacks or finalizers can release an encoder, decoder, or decoded chunk while a read or write still needs it. This can crash the interpreter. Check that a decoder is still available after reading, keep codecs alive across calls, and read the chunk length before transferring ownership. Also recheck StringIO after converting the truncate size because __index__() can close the stream.
@bedevere-app bedevere-app Bot added the awaiting review label Oct 22, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 22, 2026
Fix minor safety issues #159739
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@JelleZijlstra
JelleZijlstra merged commit 665bda9 into python:main Oct 24, 2026
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@bedevere-app bedevere-app Bot removed the awaiting review label Oct 24, 2026
@JelleZijlstra JelleZijlstra added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 24, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 24, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖
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@miss-islington-app

miss-islington-app Bot commented Oct 24, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖
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@miss-islington-app

miss-islington-app Bot commented Oct 24, 2026

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Sorry, @jelle-openai and @JelleZijlstra, 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 665bda98e861aad314457481a25f9406dedc122b 3.14
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@miss-islington-app miss-islington-app Bot assigned JelleZijlstra Oct 24, 2026
@bedevere-app

bedevere-app Bot commented Oct 24, 2026

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GH-160623 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 Oct 24, 2026
JelleZijlstra added a commit that referenced this pull request Nov 2, 2026
@miss-islington @jelle-openai @JelleZijlstra
[3.15] gh-159739: Keep text I/O state valid across reentrant callbacks (
0262ca1 
GH-160398) (#160623)

A raw read can reinitialize a TextIOWrapper as write-only, and codec callbacks or finalizers can release an encoder, decoder, or decoded chunk while a read or write still needs it. This can crash the interpreter. Check that a decoder is still available after reading, keep codecs alive across calls, and read the chunk length before transferring ownership. Also recheck StringIO after converting the truncate size because __index__() can close the stream.
(cherry picked from commit 665bda9)

Co-authored-by: Jelle Zijlstra <[email protected]>
Co-authored-by: Jelle Zijlstra <[email protected]>
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