Type hint for two classes that have themselves as element from two diferent files

Question

I have two classes from two different files.

I want to use type hints to make it easier to use.

from b import ClassB

# a.py
class ClassA():
    b: ClassB
    def __init__(self):
        self.b = None

from a import ClassA

# b.py
class ClassB():
    a: ClassA
    def __init__(self):
        self.a = None

But I run into a circular dependency problem

this doesn't work either because ClassA is not defined in this file

# b.py
class ClassB():
    a: "ClassA"
    def __init__(self):
        self.a = None