упрлс.py

import inspect
from dataclasses import dataclass, field


class Union(type):
    def __new__(cls, name, bases, namespace, **kwds):
        print('Init new Union')
        new_namespace = {}
        for attr_name, value in namespace.items():
            print(name, value)
            if inspect.isclass(value):
                exc_inherit = type(value.__name__, (value, BaseException), {})
                new_namespace[attr_name] = dataclass(exc_inherit)
                # new_namespace[name] = dataclass(value)
                new_namespace['is' + attr_name] = lambda arg: isinstance(arg, value)
            else:
                new_namespace[attr_name] = value
        result = type.__new__(cls, name, bases, new_namespace)
        return result

    def raise_type(cls, value):
        raise value


class JSON(metaclass=Union):
    class Str:
        value: str

    class Name:
        value: str

    class Dict:
        value: dict

    class List:
        value: list


jstr = JSON.Str('some text')
jlist = JSON.List([
    JSON.Str('list entry')
])


if JSON.isStr(jstr):
    print('Str:', jstr.value)
if JSON.isList(jlist):
    print('List:', jstr.value)


try:
    JSON.raise_type(jlist)
except JSON.Str as v:
    print('Str:', v)
except JSON.List as v:
    print('List:', v)