8000 Narrow `is` with final types correctly by arvi18 · Pull Request #6 · coderabbit-test/mypy · GitHub
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Narrow is with final types correctly #6

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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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Narrow is with final types correctly
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@sobolevn
sobolevn committed Jul 12, 2023
commit 99d4465bbb8026525ba54d82b47b02fb0fff4158
4 changes: 4 additions & 0 deletions mypy/subtypes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1782,6 +1782,10 @@ def covers_at_runtime(item: Type, supertype: Type) -> bool:
item = get_proper_type(item)
supertype = get_proper_type(supertype)

if isinstance(item, (CallableType, TypeType)) and item.is_singleton_type():
if is_proper_subtype(item, supertype):
return True
Comment on lines +1968 to +1970
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medium

This condition checks if the item is a singleton type and a proper subtype of the supertype. Can you add a comment explaining what a singleton type is in this context, and why this check is needed?

Suggested change
if isinstance(item, (CallableType, TypeType)) and item.is_singleton_type():
if is_proper_subtype(item, supertype):
return True
# Check if the item is a singleton type (e.g., `None`, final classes)
# and a proper subtype of the supertype.
if isinstance(item, (CallableType, TypeType)) and item.is_singleton_type():
if is_proper_subtype(item, supertype):


# Since runtime type checks will ignore type arguments, erase the types.
supertype = erase_type(supertype)
if is_proper_subtype(
Expand Down
9 changes: 9 additions & 0 deletions mypy/types.py
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Expand Up @@ -2085,6 +2085,9 @@ def with_unpacked_kwargs(self) -> NormalizedCallableType:
)
)

def is_singleton_type(self) -> bool:
return self.is_type_obj() and self.type_object().is_final

def __hash__(self) -> int:
# self.is_type_obj() will fail if self.fallback.type is a FakeInfo
if isinstance(self.fallback.type, FakeInfo):
Expand Down Expand Up @@ -2856,6 +2859,12 @@ def __eq__(self, other: object) -> bool:
return NotImplemented
return self.item == other.item

def is_singleton_type(self) -> bool:
return (
(isinstance(self.item, Instance) and self.item.type.is_final)
or isinstance(self.item, NoneType)
)

def serialize(self) -> JsonDict:
return {".class": "TypeType", "item": self.item.serialize()}

Expand Down
76 changes: 76 additions & 0 deletions test-data/unit/check-narrowing.test
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Expand Up @@ -1269,3 +1269,79 @@ def g() -> None:
def foo(): ...
foo()
[builtins fixtures/dict.pyi]


[case testNarrowingIsFinalType]
from typing import Type, Union
from typing_extensions import final

@final
class Mark: ...

@final
class Other: ...

x: Union[Type[Mark], Type[Other], Type[None], int]

if x is Mark:
reveal_type(x) # N: Revealed type is "Type[__main__.Mark]"
else:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Other], Type[None], builtins.int]"

if x is not Mark:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Other], Type[None], builtins.int]"
else:
reveal_type(x) # N: Revealed type is "Type[__main__.Mark]"

y: Type[Mark] = Mark
if x is y:
reveal_type(x) # N: Revealed type is "Type[__main__.Mark]"
else:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Other], Type[None], builtins.int]"

if x is not y:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Other], Type[None], builtins.int]"
else:
reveal_type(x) # N: Revealed type is "Type[__main__.Mark]"

if x is type(None):
reveal_type(x) # N: Revealed type is "Type[None]"
else:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[__main__.Other], builtins.int]"

if x is not type(None):
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[__main__.Other], builtins.int]"
else:
reveal_type(x) # N: Revealed type is "Type[None]"

z: Type[None]
if x is z:
reveal_type(x) # N: Revealed type is "Type[None]"
else:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[__main__.Other], builtins.int]"

if x is not z:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[__main__.Other], builtins.int]"
else:
reveal_type(x) # N: Revealed type is "Type[None]"
[builtins fixtures/isinstancelist.pyi]


[case testNarrowingIsRegualType]
from typing import Type, Union

class Mark: ...

x: Union[Type[Mark], Type[None], int]

if x is Mark:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[None], builtins.int]"
else:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[None], builtins.int]"

y: Type[Mark] = Mark
if x is y:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[None], builtins.int]"
else:
reveal_type(x) # N: Revealed type is "Union[Type[__main__.Mark], Type[None], builtins.int]"
[builtins fixtures/isinstancelist.pyi]
0