8000 Narrow `is` with final types correctly by sobolevn · Pull Request #15646 · python/mypy · GitHub
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Narrow is with final types correctly #15646

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99d4465
Narrow `is` with final types correctly
sobolevn Jul 12, 2023
0076ae8
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jul 12, 2023
a0308bc
Address primer output
sobolevn Jul 12, 2023
2fcace1
Merge branch 'master' into issue-15553
hauntsaninja Oct 17, 2024
2372c12
Update test-data/unit/check-narrowing.test
hauntsaninja Oct 17, 2024
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Address primer output
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@sobolevn
sobolevn committed Jul 12, 2023
commit a0308bcde13e907e6dd0139f031df9956913bdd1
6 changes: 6 additions & 0 deletions mypy/subtypes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1782,6 +1782,12 @@ def covers_at_runtime(item: Type, supertype: Type) -> bool:
item = get_proper_type(item)
supertype = get_proper_type(supertype)

# Left `Any` or `Type[Any]` type will never be covered at runtime:
if isinstance(item, AnyType) or (
isinstance(item, TypeType) and isinstance(item.item, AnyType)
):
return False

if isinstance(item, (CallableType, TypeType)) and item.is_singleton_type():
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What if the RHS of the is operator is a specialized generic class like list[int]? The is conditional will always evaluate to False then.

if is_proper_subtype(item, supertype):
return True
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22 changes: 22 additions & 0 deletions test-data/unit/check-narrowing.test
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Expand Up @@ -1327,6 +1327,28 @@ else:
[builtins fixtures/isinstancelist.pyi]


[case testNarrowingAnyAgainstFinalType]
from typing import Type, Any
from typing_extensions import final

@final
class Mark: ...

x: Any
if x is Mark:
reveal_type(x) # N: Revealed type is "def () -> __main__.Mark"
else:
reveal_type(x) # N: Revealed type is "Any"

y: Type[Any]
if y is Mark:
reveal_type(y) # N: Revealed type is "Type[__main__.Mark]"
else:
reveal_type(y) # N: Revealed type is "Type[Any]"

[builtins fixtures/isinstancelist.pyi]


[case testNarrowingIsRegualType]
from typing import Type, Union

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