Fall back to a higher pickle protocol when protocol 0 fails - #327
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Compiler.pickle() built the candidate list eagerly for both protocol 0 and MAX_PROTOCOL, so a form that protocol 0 cannot represent at all raised before the higher protocol was ever tried. An object of a class defining __slots__ without __getstate__ is the reported case: pickle handles it fine at protocol 5, but the compiler emitted a CompileError. Each protocol is now attempted independently and only the ones that succeed are considered. If none succeed the pickling error is re-raised so genuinely unpicklable forms still fail as before. Adds a regression test for the __slots__ case. Closes gilch#291
Owner
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Check seems to be stuck. I'll try reopening. |
Owner
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Reopened to restart Actions. |
gilch
requested changes
Aug 1, 2026
A local lambda raises AttributeError rather than PicklingError on some CPython versions, so assert against a class whose __reduce__ returns a non-tuple, which every protocol rejects with PicklingError.
gilch
approved these changes
Aug 3, 2026
Owner
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I should probably mention this in the changelog. |
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Closes #291
Compiler.pickle()built its candidate list eagerly for protocol 0 andMAX_PROTOCOL, so a form protocol 0 cannot represent — an object of a class defining__slots__without__getstate__— raised before the higher protocol was tried. Each protocol is now attempted independently and only the successful ones are candidates; if none succeed the pickling error is re-raised, so genuinely unpicklable forms still fail as before.Regression test added in
tests/test_compiler.py; it fails on master (SyntaxErrorfrom the CompileError comment) and passes with the fix. Black clean; the rest of the suite is unchanged from baseline.This change was prepared with AI assistance; the regression test was run locally and fails without the fix.