python中,同文件的类如何循环引用

Question

class A:
    def __init__(self, name: str, hello: B = None) -> None:
        self.name = name
        self.hello = hello


class B:
    def __init__(self, name: str, hello: A = None) -> None:
        self.name = name
        self.hello = hello


if __name__ == "__main__":
    a = A("h1")
    b = B("h2", a)
    c = A("h3", b)

我直接使用是报错的

Answer 1

把类名改成str型放到一个list里，遍历list使用exec来调用