def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def __init__(self, name: str, get_converter: t.Optional[t.Callable] = None) -> None:
        self.__name__ = name
        self.get_converter = get_converter