Question :
I want to allow type hinting using Python 3 to accept sub classes of a certain class. E.g.:
class A:
pass
class B(A):
pass
class C(A):
pass
def process_any_subclass_type_of_A(cls: A):
if cls == B:
# do something
elif cls == C:
# do something else
Now when typing the following code:
process_any_subclass_type_of_A(B)
I get an PyCharm IDE hint ‘Expected type A, got Type[B] instead.’
How can I change type hinting here to accept any subtypes of A?
According to this (https://www.python.org/dev/peps/pep-0484/#type-definition-syntax, “Expressions whose type is a subtype of a specific argument type are also accepted for that argument.”), I understand that my solution (cls: A) should work?
Answer #1:
When you specify cls: A, you’re saying that cls expects an instance of type A. The type hint to specify cls as a class object for the type A (or its subtypes) uses typing.Type.
from typing import Type
def process_any_subclass_type_of_A(cls: Type[A]):
pass
From The type of class objects
:
Sometimes you want to talk about class objects that inherit from a
given class. This can be spelled asType[C]whereCis a class. In
other words, whenCis the name of a class, usingCto annotate an
argument declares that the argument is an instance ofC(or of a
subclass ofC), but usingType[C]as an argument annotation declares
that the argument is a class object deriving fromC(orCitself).
