Subclass in type hinting

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?

(cls: A)

2 Answers
2

When you do cls: A, you're saying that cls is going to an instance of type A. To make it work with type or its subtypes use typing.Type.

cls: A

cls

A

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 as Type[C] where C is a class. In
other words, when C is the name of a class, using C to annotate an
argument declares that the argument is an instance of C (or of a
subclass of C), but using Type[C] as an argument annotation declares
that the argument is a class object deriving from C (or C itself).

Type[C]

C

C

C

C

C

Type[C]

C

C

I found the soluton. Use:

from typing import Type
def process_any_subclass_type_of_A(cls: Type[A]):
pass


And the desired behavior will be there as noted in the PEP above.

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