infer x: T if x.__class__: type[T] #1163
Description
Describe the Bug
So if e.g. x.__class__ is int, then narrow x: int:
from typing import reveal_type
def g(x):
assert x.__class__ is int
reveal_type(x) # revealed type: Unknown (_.__class__: type[int])(sandbox)
Here's a structural use-case:
from typing import Protocol, final
@final
class JustInt(Protocol):
@property
def __class__(self, /) -> type[int]: ...
@__class__.setter
def __class__(self, t: type[int], /) -> None: ...
def assert_int(x: JustInt, /) -> int:
assert isinstance(x, int) # should not be needed
return x
assert_int(42) # correctly accepted
assert_int(False) # correctly rejected ;)(sandbox)
Another interesting use-case is emulating the intersection of a structural and a nominal type:
from typing import Protocol, final
class Thing: ...
class IntThing(Thing):
def __int__(self) -> int: return 42
class FloatThing(Thing):
def __float__(self) -> float: return 42
@final
class ThingThatSupportsFloat(Protocol):
@property
def __class__(self, /) -> type[Thing]: ...
def __float__(self, /) -> float: ...So this would make ThingThatSupportsFloat equivalent to Thing & typing.SupportsFloat. That should take care of many (if not most) of the intersection-type use-cases, for free basically.
Sandbox Link
No response
(Only applicable for extension issues) IDE Information
No response