Remove obsolete Literal deduplication assertion - #785
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Codecov Report✅ All modified and coverable lines are covered by tests. @@ Coverage Diff @@
## main #785 +/- ##
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- Coverage 97.26% 97.26% -0.01%
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Files 3 3
Lines 7860 7859 -1
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- Hits 7645 7644 -1
Misses 215 215
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AlexWaygood
marked this pull request as ready for review
August 12, 2026 11:56
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Fixes #784.
Summary
Remove the assertion that
Literal[[], []].__args__is([], []). python/cpython#153914 deliberately changedtyping.Literalto deduplicate unhashable arguments, so Python 3.14.7 now returns([],)instead. On supported Python versions wheretyping_extensions.Literalaliasestyping.Literal, the old assertion therefore contradicts the standard library behavior.This PR just deletes the assertion entirely: the behaviour here is now version-dependent, and the assertion was always testing an implementation detail that wasn't really that important.
Historical context
typing_extensionsin Fix various things withLiteral#145. That PR addressed (🐞)Literaldoesn't flatten it's arguments #113 and backported bpo-42345: Fix three issues with typing.Literal parameters cpython#23294 and bpo-42345: Fix hash implementation of typing.Literal cpython#23383. The assertion was copied verbatim with the rest of CPython'sLiteralTests.test_argsin the first commit of that PR. There was no discussion about this particular assertion on Fix various things withLiteral#145.Union, and Guido asked whether mutableLiteralarguments were actually valid.Literalarguments at type-checking time but intentionally does not validate them at runtime. The CPython reviewers therefore agreed not to deduplicate mutable arguments. Guido subsequently requested explicit__args__coverage, and commit f653d680 introduced the exact assertion that Fix various things withLiteral#145 later copied.typing_extensionsimplementation bug.