Fix spurious possibly-undefined errors in for-else with break #19696
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When a for loop contains branches with `break` and an `else` block, variables declared inside those branches were incorrectly discarded from further analysis, leading Mypy to incorrectly report a variable as undefined after the loop or as used before declaration. With this fix, when a for loop's `else` block is considered, variables declared in every branch of the `for` loop body that called `break` are now considered as defined within the body of the loop. Fixes python#14209 Fixes python#19690
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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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@ilevkivskyi, I asked you for review since you reviewed the original change three years back. |
ilevkivskyi
approved these changes
Aug 25, 2025
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| raise RuntimeError | ||
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| print(value) # Should not error - value is defined if we broke |
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Maybe also add one two tests where it should error? Like, e.g, if raise above is conditional.
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Good idea, I will add the test.
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When a for loop contains branches with
breakand anelseblock, variables declared inside those branches were incorrectly discarded from further analysis, leading Mypy to incorrectly report a variable as undefined after the loop or as used before declaration.With this fix, when a for loop's
elseblock is considered, variables declared in every branch of theforloop body that calledbreakare now considered as defined within the body of the loop.Fixes #14209
Fixes #19690