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GeezerVison is showing github.com — gh-156939: Fix two bugs in PyBytesWriter by vstinner · Pull Request #158404 · python/cpython

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@vstinner

@vstinner vstinner commented Sep 29, 2026 •
edited by bedevere-app Bot
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Fix PyBytesWriter_Format() error handling: restore the writer to its previous state on error. Add an unit test injecting MemoryError.

Fix PyBytesWriter_FinishWithSize() to return an empty bytearray when use_bytearray is set and size is 0, instead of always returning an empty bytes object.

Fix test_capi.test_bytes: always check writer finish result type, to make sure that _PyBytesWriter_CreateByteArray() always create bytearray objects.

  • Issue: C API: Detect buffer overflow in PyBytesWriter #156939

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@vstinner @claude
pythongh-156939: Fix two bugs in PyBytesWriter
ed1785f 
Fix PyBytesWriter_Format() error handling: restore the writer to its
previous state on error. Add an unit test injecting MemoryError.

Fix PyBytesWriter_FinishWithSize() to return an empty bytearray when
use_bytearray is set and size is 0, instead of always returning an
empty bytes object.

Fix test_capi.test_bytes: always check writer finish result type, to
make sure that _PyBytesWriter_CreateByteArray() always create
bytearray objects.

Co-Authored-By: Claude Opus 4.6 <[email protected]>
@vstinner vstinner added the skip news label Sep 29, 2026
@bedevere-app bedevere-app Bot added the type-feature A feature request or enhancement label Sep 29, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Sep 29, 2026
C API: Detect buffer overflow in PyBytesWriter #156939
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@bedevere-app bedevere-app Bot added the awaiting core review label Sep 29, 2026
@vstinner vstinner added the needs backport to 3.15 bugs and security fixes label Sep 29, 2026
@vstinner

vstinner commented Sep 29, 2026

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The "Android aarch64" job failed with a download error: Command "curl -Lf --retry 5 --retry-all-errors -o /Users/runner/work/cpython/cpython/cross-build/downloads/xz-5.4.6-1-aarch64-linux-android.tar.gz https://github.com/beeware/cpython-android-source-deps/releases/download/xz-5.4.6-1/xz-5.4.6-1-aarch64-linux-android.tar.gz" returned exit status 56. I restarted the job.
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@vstinner vstinner removed the type-feature A feature request or enhancement label Sep 29, 2026
@vstinner
vstinner merged commit 24ea85a into python:main Sep 29, 2026
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@vstinner
vstinner deleted the fix_writer branch September 29, 2026 12:50
@miss-islington-app

miss-islington-app Bot commented Sep 29, 2026

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Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖
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@bedevere-app bedevere-app Bot removed the awaiting core review label Sep 29, 2026
@miss-islington-app

miss-islington-app Bot commented Sep 29, 2026

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Sorry, @vstinner, I could not cleanly backport this to 3.15 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 24ea85a4c2998b36cc4c83ff0505678d178b49d1 3.15
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@miss-islington-app miss-islington-app Bot assigned vstinner Sep 29, 2026
@bedevere-app

bedevere-app Bot commented Sep 29, 2026

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GH-158409 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 Sep 29, 2026
hugovk pushed a commit that referenced this pull request Sep 30, 2026
@vstinner @claude
[3.15] gh-156939: Fix two bugs in PyBytesWriter (#158404) (#158409)
3740f74 
* gh-156939: Fix two bugs in PyBytesWriter (#158404)

Fix PyBytesWriter_Format() error handling: restore the writer to its
previous state on error. Add an unit test injecting MemoryError.

Fix PyBytesWriter_FinishWithSize() to return an empty bytearray when
use_bytearray is set and size is 0, instead of always returning an
empty bytes object.

Fix test_capi.test_bytes: always check writer finish result type, to
make sure that _PyBytesWriter_CreateByteArray() always create
bytearray objects.

Co-authored-by: Claude Opus 4.6 <[email protected]>
(cherry picked from commit 24ea85a)
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@vstinner
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