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GeezerVison is showing github.com — gh-159739: Keep the instance type alive during ABC subclass checks by jelle-openai · Pull Request #160198 · 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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When an instance advertises a __class__ different from its actual type, ABCMeta.__instancecheck__ performs two subclass checks. The first callback can change the instance's actual type and allow its old type to be collected before the second check, causing a crash. Keep the original type alive through both checks. Backport to 3.15 and 3.14.

  • Issue: Fix minor safety issues #159739

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@jelle-openai
pythongh-159739: Keep the instance type alive during ABC subclass checks
8ff2889 
When an instance advertises a __class__ different from its actual type, ABCMeta.__instancecheck__ performs two subclass checks. The first callback can change the instance's actual type and allow its old type to be collected before the second check, causing a crash. Keep the original type alive through both checks. Backport to 3.15 and 3.14.
@bedevere-app bedevere-app Bot mentioned this pull request Oct 22, 2026
Fix minor safety issues #159739
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@bedevere-app bedevere-app Bot added the awaiting review label Oct 22, 2026
@JelleZijlstra
JelleZijlstra merged commit dcbc453 into python:main Oct 22, 2026
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@JelleZijlstra JelleZijlstra added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 22, 2026
@bedevere-app bedevere-app Bot removed the awaiting review label Oct 22, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 22, 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 22, 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 22, 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, 3.15.
🐍🍒⛏🤖
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@miss-islington-app

miss-islington-app Bot commented Oct 22, 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 dcbc45356ea7ccc8038f40dd293f0e338f5ff977 3.14
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@miss-islington-app miss-islington-app Bot assigned JelleZijlstra Oct 22, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 22, 2026

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Sorry, @jelle-openai and @JelleZijlstra, I could not cleanly backport this to 3.15 due to a conflict.

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

cherry_picker dcbc45356ea7ccc8038f40dd293f0e338f5ff977 3.15
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@miss-islington-app

miss-islington-app Bot commented Oct 22, 2026

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Sorry, @jelle-openai and @JelleZijlstra, I could not cleanly backport this to 3.15 due to a conflict.

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

cherry_picker dcbc45356ea7ccc8038f40dd293f0e338f5ff977 3.15
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@miss-islington-app

miss-islington-app Bot commented Oct 22, 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 dcbc45356ea7ccc8038f40dd293f0e338f5ff977 3.14
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This was referenced Oct 23, 2026
[3.14] gh-159739: Keep the instance type alive during ABC subclass checks (GH-160198) #160488
Merged
[3.15] gh-159739: Keep the instance type alive during ABC subclass checks (GH-160198) #160489
Merged
@bedevere-app

bedevere-app Bot commented Oct 23, 2026

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GH-160488 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 Oct 23, 2026
@bedevere-app

bedevere-app Bot commented Oct 23, 2026

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GH-160489 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 23, 2026
JelleZijlstra pushed a commit that referenced this pull request Oct 24, 2026
@jelle-openai
[3.14] gh-159739: Keep the instance type alive during ABC subclass ch…
605d611 
…ecks (GH-160198) (#160488)

When an instance advertises a __class__ different from its actual type, ABCMeta.__instancecheck__ performs two subclass checks. The first callback can change the instance's actual type and allow its old type to be collected before the second check, causing a crash. Keep the original type alive through both checks. Backport to 3.15 and 3.14.
(cherry picked from commit dcbc453)
JelleZijlstra pushed a commit that referenced this pull request Oct 24, 2026
@jelle-openai
[3.15] gh-159739: Keep the instance type alive during ABC subclass ch…
e736c96 
…ecks (GH-160198) (#160489)

When an instance advertises a __class__ different from its actual type, ABCMeta.__instancecheck__ performs two subclass checks. The first callback can change the instance's actual type and allow its old type to be collected before the second check, causing a crash. Keep the original type alive through both checks. Backport to 3.15 and 3.14.
(cherry picked from commit dcbc453)
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@jelle-openai @JelleZijlstra
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