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Types should be promoted by issubclass #2909
Description
I expected types to be promoted to sub-types within an issubclass block, the same as instances within an isinstance block, but type-checking the following code results in the error Type[Vehicle] has no attribute "wheels":
from typing import Type
class Vehicle(object):
name = ''
class Car(Vehicle):
wheels = 4
def test_isinstance(x):
# type: (Vehicle) -> None
print(x.name)
if isinstance(x, Car):
print(x.wheels)
def test_issubclass(x):
# type: (Type[Vehicle]) -> None
print(x.name)
if issubclass(x, Car):
print(x.wheels)Is this be possible or am I missing something? I'm testing against the master branch.
Activity
ilevkivskyi commentedon Feb 26, 2017
This would be an interesting feature. Also I think the implementation would be straightforward, since
isinstanceis already understood by mypy.JukkaL commentedon Feb 27, 2017
Yeah, this would be a reasonable thing to support, though you can currently work around the limitation pretty easily by using
cast(Type[Subclass], x)after theissubclasscheck. Example: