Implement TypeIs (PEP 742) #16898
Implement TypeIs (PEP 742) #16898
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| return {expr: TypeGuardedType(node.callee.type_guard)}, {} | ||
| else: | ||
| assert node.callee.type_is is not None | ||
| return conditional_types_to_typemaps( |
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This is the crucial part of the change, which implements the new type narrowing behavior. It's the same as isinstance(), a little way up in the same method.
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Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>
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Thanks for the review! I applied the suggestions, and will deal with the larger issues in the next few days. |
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Missed commenting on the PR title earlier. Could you update it to mention |
JelleZijlstra
changed the title
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mypy/errorcodes.py
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| @@ -281,5 +281,11 @@ def __hash__(self) -> int: | |||
| sub_code_of=MISC, | |||
| ) | |||
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| TYPE_NARROWER_NOT_SUBTYPE: Final[ErrorCode] = ErrorCode( | |||
| "type-is-not-subtype", | |||
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I propose type-narrower-not-subtype, right now this error code can be misleading for readers: type is not a subtype?
It would be consistent with:
TYPE_NARROWER_NOT_SUBTYPE: Final = ErrorMessage(
"Narrowed type {} is not a subtype of input type {}", codes.TYPE_NARROWER_NOT_SUBTYPE
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Maybe narrowed-type-not-subtype? Your suggestion sounds like TypeNarrower, which was a rejected name for teh feature.
test-data/unit/check-typeis.test
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| g(reveal_type(x)) # N: Revealed type is "Union[builtins.list[builtins.str], __main__.<subclass of "list" and "A">]" | ||
| [builtins fixtures/tuple.pyi] | ||
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| [case testTypeIsMultipleCondition-xfail] |
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Can you please add a comment on why this is marked as xfail?
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I copied this from the TypeGuard test. Seems like the xfail is just because we generate a name with an extra 1 at the end, which looks like a typo:
Expected:
main:16: note: Revealed type is "__main__.<subclass of "Foo" and "Bar">"
main:21: note: Revealed type is "__main__.<subclass of "Foo" and "Bar">" (diff)
Actual:
main:16: note: Revealed type is "__main__.<subclass of "Foo" and "Bar">"
main:21: note: Revealed type is "__main__.<subclass of "Foo" and "Bar">1" (diff)
I will remove the xfail and make it pass.
| from typing import Callable, List, TypeVar | ||
| from typing_extensions import TypeIs | ||
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| A = Callable[[object], TypeIs[List[T]]] |
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T is not defined, why does this test pass?
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This is a general issue with test cases that I've seen in other tests as well. I'm not sure if T is coming from the builtins stubs or whatever else. If you are really interested I could quickly try and search where this has happened.
Obviously still good to point it out and change it here.
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I think the root cause of this is that a normal builtins.pyi in typeshed defined _T (which does not get exported) wheres the test fixtures (like dict.pyi) typically use stuff like T (which does get exported).
It would probably be a good idea to change all fixtures, but that might be quite a bit of work.
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Added an explicit definition of T in this test. Agree that ideally we should fix this throughout the test suite.
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And don't forget to add a new code to https://github.com/python/mypy/blob/master/test-data/unit/check-errorcodes.test |
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Thanks @sobolevn! I have pushed some changes to address your review. |
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Diff from mypy_primer, showing the effect of this PR on open source code: graphql-core (https://github.com/graphql-python/graphql-core)
+ src/graphql/execution/execute.py:638: error: Unused "type: ignore" comment [unused-ignore]
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| @@ -1018,10 +1018,22 @@ def visit_callable_type(self, template: CallableType) -> list[Constraint]: | |||
| param_spec = template.param_spec() | |||
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| template_ret_type, cactual_ret_type = template.ret_type, cactual.ret_type | |||
| if template.type_guard is not None: | |||
| if template.type_guard is not None and cactual.type_guard is not None: | |||
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Nice, thanks! I think this should fix a thing I ran into while testing #16939
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Thanks again, one last suggestion: we can add a test case to check-incremental to ensure that cache works correctly for type narrowing. Especially, because TypeGuard is also missing from there: https://github.com/python/mypy/blob/master/test-data/unit/check-incremental.test
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Thanks! I'll work on a separate PR with incremental tests for both TypeGuard and TypeIs. |
Cross-ref python/peps#3649.