Subclass in type hinting

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Question :

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:

class B(A):

class C(A):

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:


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 (, “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]):

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).

Answered By: Ashwini Chaudhary

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