confusion_annotation_mypy.py

from typing import Union

class A():
    a: int = 0
    b: int = 0

class B():
    a: int = 0
    b: int = 0

def a_function(variable: Union[A, B]):
    print("class provided is " + str(variable))


my_shortcut_union_type = Union[A, B]


def a_function_(variable: my_shortcut_union_type):
    print("provided is " + str(variable))


a_function(A)  # ERROR
a = A()
a_function(a)  # OKAY