from typing import Annotated, get_type_hints

class Parent:
    def __init__(self, num: int) -> None:
        self.num = num

class Foo(Parent):
    # Realization of hashable protocol: https://docs.python.org/3.12/glossary.html#term-hashable
    def __eq__(self, other):
        if not isinstance(other, Parent):
            return NotImplemented
        return self.num == other.num
    def __hash__(self):
        return hash(self.num)

class Bar(Parent):  # Same realization of __eq__ and __hash__ as in Foo but semantically it's another class :)
    def __eq__(self, other):
        if not isinstance(other, Parent):
            return NotImplemented
        return self.num == other.num
    def __hash__(self):
        return hash(self.num)

class Form:
    box_a: Annotated[str, Foo(1)]

class Message:
    field_a: Annotated[str, Bar(1)]

hints = get_type_hints(Message, include_extras=True)
metadata = hints["field_a"].__metadata__[0]
print(f"MessageCode metadata type: {type(metadata)}")

hints = get_type_hints(Form, include_extras=True)
metadata = hints["box_a"].__metadata__[0]
print(f"DisplayName metadata type: {type(metadata)}")

MessageCode metadata type: <class '__main__.Foo'>
DisplayName metadata type: <class '__main__.Foo'>

>>> hints = get_type_hints(Message, include_extras=True)
>>> metadata = hints["field_a"].__metadata__[0]
>>> print(f"MessageCode metadata type: {type(metadata)}")
MessageCode metadata type: <class '__main__.MessageCode'>
>>> 
>>> hints = get_type_hints(Form, include_extras=True)
>>> metadata = hints["box_a"].__metadata__[0]
>>> print(f"DisplayName metadata type: {type(metadata)}")
DisplayName metadata type: <class '__main__.DisplayName'>