GeezerVison is showing github.com — [3.14] gh-159739: Keep the instance type alive during ABC subclass checks (GH-160198) by jelle-openai · Pull Request #160488 · python/cpython
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Oct 23, 2026
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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.
(cherry picked from commit dcbc453)
Co-authored-by: Jelle Zijlstra [email protected]
Backport of #160198 to 3.14.
Carry over the subclass-callback lifetime fix and its regression test, adapting the test imports to the release branch.
Ran test_abc on a free-threaded 3.14 build.
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…ass checks (pythonGH-160198)
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)
Co-authored-by: Jelle Zijlstra <[email protected]>
This was referenced Oct 23, 2026
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