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gh-159283: Keep the propagating exception in PyObject_ClearManagedDict() - #159284
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christianaurichzm wants to merge 1 commit into
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…gedDict() When an object whose __dict__ still pointed at its inline values was freed while an exception was propagating, a failed allocation while detaching the dict called PyErr_NoMemory(), which replaced that exception, and PyErr_FormatUnraisable() then cleared it. A debug build aborted in py_dealloc() and a release build went on with no exception set, which ended in SystemError. Save the current exception before detaching the dict and restore it afterwards.
christianaurichzm
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markshannon and
methane
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October 13, 2026 02:28
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Fixes #159283
PyObject_ClearManagedDict()runs when an object is freed. If the object's__dict__has been materialized but still points at the inline values, it callsdetach_dict_from_object(), which callsPyErr_NoMemory()whencopy_values()fails. When the object is freed while an exception is propagating, for example a temporary on the evaluation stack during unwinding, thatMemoryErrorreplaces the propagating exception, and thePyErr_FormatUnraisable()call that follows clears it. A debug build aborts inpy_dealloc(), and a release build goes on with no exception set and ends inSystemError('error return without exception set').This change saves the current exception with
PyErr_GetRaisedException()before detaching the dict and restores it afterwards. TheMemoryErroris still reported as unraisable, and the original exception keeps propagating. The extra calls are only on the path that detaches a materialized dict.The same code is in 3.14 and 3.15.
Verification
test_classaborts an unpatched debug build withFatal Python error: py_dealloc: Deallocator of type 'A' cleared the current exceptionand passes with the fix. The reproducer from the issue getsSystemErroron an unpatched release build andZeroDivisionErrorwith the fix.test_class,test_dict,test_capi.test_dict,test_descr,test_gc,test_exceptionsandtest_unittestpass on a debug build, and the new test passes with-R 3:3.