Python のジェネリック型から実行時に型パラメータを取得する方法

from typing import Generic, TypeVar

T = TypeVar("T")

class MyList(Generic[T]):
    ...

ints = MyList[int]()

import types
from typing import Generic, TypeVar, Any

T = TypeVar("T")

class Reified(Generic[T]):

    type_arg: Any = Any

    def __class_getitem__(cls, key):
        reified = types.new_class(
            name=cls.__name__,
            bases=(cls,),
            exec_body=(lambda ns: ns)
        )
        reified.type_arg = key
        return reified

class MyStack(Reified[T]):

    def __init__(self) -> None:
        super().__init__()
        self.items: list[T] = []

    def push(self, item: T) -> None:
        # 実行時に型を調べて、非許容な値の場合はエラーにする
        if isinstance(item, self.type_arg):
            self.items.append(item)
        else:
            raise TypeError()

    def pop(self) -> T:
        if self.items:
            return self.items.pop()
        else:
            raise IndexError("pop from empty stack")

>>> MyStack[int]().push(100)
>>> MyStack[int]().push(0.1)
TypeError
>>> MyStack[int]().push("aaa")
TypeError

>>> s = MyStack[int]()
>>> isinstance(s, Generic)
True
>>> isinstance(s, Reified)
True
>>> isinstance(s, MyStack)
True
>>> isinstance(s, MyStack[int])  # 上記で述べたクラスの同一性を直せば True になる
False
>>> isinstance(s, MyStack[str])
False

>>> issubclass(MyStack, Generic)
True
>>> issubclass(MyStack, Reified)
True
>>> issubclass(MyStack, MyStack[int])
False
>>> issubclass(MyStack[int], MyStack)
True