Make optional type narrowing actually optional in tuples_type_compat.py #1981
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I agree these should be marked with "E?" rather than "E" because they are optional in the spec. Thanks for the fix. |
erictraut
approved these changes
Apr 22, 2025
| @@ -71,15 +71,15 @@ def func4( | |||
| def func5(val: tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]): | |||
| if len(val) == 1: | |||
| # Type can be narrowed to tuple[int]. | |||
| assert_type(val, tuple[int]) # tuple[int] | |||
| assert_type(val, tuple[int]) # E?: tuple[int] | |||
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This makes the test not very useful (without manual review) since type checkers will now pass no matter what type they infer for val. One solution could be to use two types and asserts that exactly one of them errors, by using an error group and asserting for both the narrowed and non-narrowed type. However, we don't currently check in that case that there is exactly one error. I can send a PR doing that.
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Sounds reasonable to me.
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This pull request marks optional type narrowing in tuples_type_compat.py with
E?to signify its optionality. Otherwise, it is treated as obligatory.See the comment
NOTE: This type narrowing functionality is optional, not mandated.at the beginning of each function.