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Further improve match statement narrowing against unions - #20744
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hauntsaninja merged 3 commits intoFeb 11, 2026
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I realised there is a simpler and more powerful approach than the one taken in python#19600. This basically adds the new "Step 2" to the original code.
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hauntsaninja
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February 5, 2026 08:24
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JukkaL
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Thanks, looks good -- just one potential code path that seems redundant.
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mypy/checkpattern.py
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| elif isinstance(current_type, AnyType): | ||
| inner_type: Type = AnyType(TypeOfAny.from_another_any, current_type) | ||
| inner_types = [inner_type] * len(o.patterns) | ||
| elif isinstance(current_type, TupleType): |
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Second check against TupleType that can never be taken?
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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This was referenced Feb 25, 2026
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Fixes #18950 Fixes this comment #19081 (comment) (previously improved on by #20744 and #20782 )
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I realised there is a simpler and more complete approach than the one taken in #19600.
This adds the new "Step 2" to the original code. Best way to review the diff is probably to check it out and review it squashed with #19600 , but really the net logic change is just "Step 2"
Fixes #15190
Fixes #17549
Fixes #17600
Mostly fixes #18039
Helps with things in #19081