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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def __get_obj_by_discriminator(self, payload, obj_type):
 # type: (str, Union[T, str]) -> T """Get correct subclass instance using the discriminator in payload. :param payload: Payload for deserialization :type payload: str :param obj_type: parent class for deserializing payload into :type obj_type: Union[object, str] :return: Subclass of provided parent class, that resolves to the discriminator in payload. :rtype: object :raises: :py:class:`ask_sdk_core.exceptions.SerializationException` """

        obj_cast = cast(Any, obj_type)
        namespaced_class_name = obj_cast.get_real_child_model(payload)
        if not namespaced_class_name:
            raise SerializationException(
                "Couldn't resolve object by discriminator type "
                "for {} class".format(obj_type))

        return self.__load_class_from_name(namespaced_class_name)