Type not narrowed correctly for if X in collection
#3229
Comments
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Than you for reporting this! I have also encountered situations where this could be useful. It is not super easy to implement, but I think this is a reasonable feature to support (especially for invariant collections, where the type is known precisely). As a workaround, you could add |
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I just realised: there might also have to be a special case for testing if a float is in a set of ints, or any other situation where |
Enables the narrowing of variable types when checking a variable is "in" a collection, and the collection type is a subtype of the variable type. Fixes #3229 This PR updates the type narrowing for the "in" operator and allows it to narrow the type of a variable to the type of the collection's items - if the collection item type is a subtype of the variable (as defined by is_subtype). Examples ```python def foobar(foo: Union[str, float]): if foo in ['a', 'b']: reveal_type(foo) # N: Revealed type is "builtins.str" else: reveal_type(foo) # N: Revealed type is "Union[builtins.str, builtins.float]" ``` ```python typ: List[Literal['a', 'b']] = ['a', 'b'] x: str = "hi!" if x in typ: reveal_type(x) # N: Revealed type is "Union[Literal['a'], Literal['b']]" else: reveal_type(x) # N: Revealed type is "builtins.str" ``` One existing test was updated, which compared `Optional[A]` with "in" to `(None,)`. Piror to this change that resulted in `Union[__main__.A, None]`, which now narrows to `None`. Test cases have been added for "in", "not in", Sets, Lists, and Tuples. I did add to the existing narrowing.pyi fixture for the test cases. A search of the *.test files shows it was only used in the narrowing tests, so there shouldn't be any speed impact in other areas. --------- Co-authored-by: Jordandev678 <20153053+Jordandev678@users.noreply.github.com>
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Reopening, since the original implementation was reverted due to some issues (#17864). |
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@JukkaL want me to pick this up? |
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@Jordandev678 Sure! The original PR can be resubmitted once the issues have been addressed. |
The revealed type is
Union[builtins.str, builtins.float]but should bebuiltins.strThe text was updated successfully, but these errors were encountered: