gh-121291: Respect mixin bitwise-operator overrides on Flag subclasses - #155862
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SomSamantray wants to merge 5 commits into
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gh-121291: Respect mixin bitwise-operator overrides on Flag subclasses#155862SomSamantray wants to merge 5 commits into
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…lasses EnumMeta.__new__ unconditionally installed Flag's __or__/__and__/__xor__/ __ror__/__rand__/__rxor__/__invert__ onto every Flag subclass, silently discarding a mixin base's own override of these dunders -- even though the class's MRO should have resolved to the mixin's method. Give this loop the same MRO-aware check already used a few lines above for __repr__/__str__/__format__/__reduce_ex__: only install Flag's method when nothing else (neither a mixin nor a mixed-in data type, e.g. IntFlag's int) already provides a real override.
Avoids redeclaring an equivalent IntFlag enum inline when OldTestIntFlag already defines and reuses one.
The fixed loop and NEWS entry cover all seven Flag operator dunders; extend the regression test to exercise the reflected forms too, per code review (ce-code-review finding python#2).
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EnumType.__new__(Lib/enum.py) installsFlag's__or__/__and__/__xor__/__ror__/__rand__/__rxor__/__invert__onto everyFlagsubclass whenever the name isn't in the subclass's own class body — but that check never looked at what a mixin base actually resolved to, soclass MyFlag(Mixin, Flag)silently lost the mixin's own operator overrides toFlag's defaults. The__repr__/__str__/__format__/__reduce_ex__block a few lines above already handles this correctly (checking whether the class's real MRO-resolved method is still the type default before overwriting); this gives the Flag-operator loop the same MRO-aware check.The check also has to distinguish a mixin's own override from a mixed-in data type's raw operator (e.g.
int.__or__forIntFlag) — an earlier version of this fix compared only againstFlag's own method and broke everyIntFlagcombination (Color.RED | Color.BLUEsilently returned a plainintinstead of a boxedIntFlag), caught by running the fulltest_enumsuite including theDoc/howto/enum.rstdoctests.Lib/test/test_enum.pygets a regression test in bothOldTestFlagandOldTestIntFlagcovering: a mixin's override winning overFlag's default (forward and reflected forms), dunders the mixin didn't touch still gettingFlag's own, and theIntFlag/intregression case. Full suite: 1091 tests pass, 0 failures.One known scope boundary, called out during review: when the overriding mixin is itself the class selected as
member_type(e.g. a customintsubclass that also overrides__or__), the identity check still can't tell that apart from the raw data-type operator — the same limitation the pre-existing__repr__/__str__block already has. Fixing that would need a heavier MRO/__dict__-walk redesign touching both blocks; out of scope here.Fixes #121291.