Python instanceof on alias type

I have the following types and type alias defined:

@unique
class MyEnum(Enum):
    A = 1
    B = 2
    C = 3
    D = 4

class A:
    pass


class B:
    pass

MyAlias = MyEnum | A | B

MyAlias2 = MyAlias | str | int

@dataclass(slots=True)
class A:
    type: MyAlias2

If I do isinstance check like so:

a = A()
isintance(a, MyAlias)

it returns False.

I understand that it happens because I redefine the class later, but I do this because I first need to define what is a type of type MyAlias so I could later define what is MyAlias2 to then be able to use it as an attribute inside class A. Now obviously since we’re in python I could just not define the attributes of class A and make a constructor that accept whatever, but since I’m thinking about portability in the future, and also I do want the "benefits" of type hinting right now, I do it this way and I wonder what can I do to make the isinstance report True in such case where there’s circular dependency between what is defined first.

>Solution :

You can define A first and use a string as the typehint.

@dataclass(slots=True)
class A:
    type: 'MyAlias'

MyAlias = MyEnum | A | B