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GeezerVison is showing github.com — [3.15] gh-159739: Keep generic alias arguments alive while formatting errors (GH-159981) by miss-islington · Pull Request #160020 · python/cpython

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@miss-islington

@miss-islington miss-islington commented Oct 21, 2026 •
edited by bedevere-app Bot
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When a generic alias contains a list of parameters and an object claiming to be an unpacked type-variable tuple returns a non-tuple from __typing_subst__, the error path frees the temporary argument tuple before reading it to format a TypeError. That use-after-free can crash the interpreter instead of reporting the invalid substitution.
(cherry picked from commit 9c649db)

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

  • Issue: Fix minor safety issues #159739

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@jelle-openai @miss-islington
pythongh-159739: Keep generic alias arguments alive while formatting …
afa398e 
…errors (pythonGH-159981)

When a generic alias contains a list of parameters and an object claiming to be an unpacked type-variable tuple returns a non-tuple from `__typing_subst__`, the error path frees the temporary argument tuple before reading it to format a `TypeError`. That use-after-free can crash the interpreter instead of reporting the invalid substitution.
(cherry picked from commit 9c649db)

Co-authored-by: Jelle Zijlstra <[email protected]>
@bedevere-app bedevere-app Bot mentioned this pull request Oct 21, 2026
gh-159739: Keep generic alias arguments alive while formatting errors #159981
Merged
@bedevere-app bedevere-app Bot added the awaiting review label Oct 21, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 21, 2026
Fix minor safety issues #159739
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@JelleZijlstra
JelleZijlstra merged commit 8411879 into python:3.15 Oct 21, 2026
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@bedevere-app bedevere-app Bot removed the awaiting review label Oct 21, 2026
@miss-islington
miss-islington deleted the backport-9c649db-3.15 branch October 21, 2026 18:50
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3 participants

@miss-islington @JelleZijlstra @jelle-openai
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