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Title: [3.14] gh-143650: Fix importlib race condition on import failure (GH-143651) by miss-islington · Pull Request #144662 · python/cpython · GitHub

Open Graph Title: [3.14] gh-143650: Fix importlib race condition on import failure (GH-143651) by miss-islington · Pull Request #144662 · python/cpython

X Title: [3.14] gh-143650: Fix importlib race condition on import failure (GH-143651) by miss-islington · Pull Request #144662 · python/cpython

Description: Fix a race condition where a thread could receive a partially-initialized module when another thread's import fails. The race occurs when: Thread 1 starts importing, adds module to sys.modules Thread 2 sees the module in sys.modules via the fast path Thread 1's import fails, removes module from sys.modules Thread 2 returns a stale module reference not in sys.modules The fix adds verification after the "skip lock" optimization in both Python and C code paths to check if the module is still in sys.modules. If the module was removed (due to import failure), we retry the import so the caller receives the actual exception from the import failure rather than a stale module reference. (cherry picked from commit ac8b5b6) Co-authored-by: Gregory P. Smith 68491+gpshead@users.noreply.github.com Co-Authored-By: Claude Opus 4.5 noreply@anthropic.com Issue: gh-143650

Open Graph Description: Fix a race condition where a thread could receive a partially-initialized module when another thread's import fails. The race occurs when: Thread 1 starts importing, adds module to sys.modules...

X Description: Fix a race condition where a thread could receive a partially-initialized module when another thread's import fails. The race occurs when: Thread 1 starts importing, adds module to sys.mod...

Opengraph URL: https://github.com/python/cpython/pull/144662

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