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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 subscribe(self, topic, qos=0):
 """Subscribe the client to one or more topics. This function may be called in three different ways: Simple string and integer e.g. subscribe("my/topic", 2) topic: A string specifying the subscription topic to subscribe to. qos: The desired quality of service level for the subscription. Defaults to 0. String and integer tuple e.g. subscribe(("my/topic", 1)) topic: A tuple of (topic, qos). Both topic and qos must be present in the tuple. qos: Not used. List of string and integer tuples e.g. subscribe([("my/topic", 0), ("another/topic", 2)]) This allows multiple topic subscriptions in a single SUBSCRIPTION command, which is more efficient than using multiple calls to subscribe(). topic: A list of tuple of format (topic, qos). Both topic and qos must be present in all of the tuples. qos: Not used. The function returns a tuple (result, mid), where result is MQTT_ERR_SUCCESS to indicate success or (MQTT_ERR_NO_CONN, None) if the client is not currently connected. mid is the message ID for the subscribe request. The mid value can be used to track the subscribe request by checking against the mid argument in the on_subscribe() callback if it is defined. Raises a ValueError if qos is not 0, 1 or 2, or if topic is None or has zero string length, or if topic is not a string, tuple or list. """

        topic_qos_list = None
        if isinstance(topic, str):
            if qos<0 or qos>2:
                raise ValueError('Invalid QoS level.')
            if topic is None or len(topic) == 0:
                raise ValueError('Invalid topic.')
            topic_qos_list = [(topic.encode('utf-8'), qos)]
        elif isinstance(topic, tuple):
            if topic[1]<0 or topic[1]>2:
                raise ValueError('Invalid QoS level.')
            if topic[0] is None or len(topic[0]) == 0 or not isinstance(topic[0], str):
                raise ValueError('Invalid topic.')
            topic_qos_list = [(topic[0].encode('utf-8'), topic[1])]
        elif isinstance(topic, list):
            topic_qos_list = []
            for t in topic:
                if t[1]<0 or t[1]>2:
                    raise ValueError('Invalid QoS level.')
                if t[0] is None or len(t[0]) == 0 or not isinstance(t[0], str):
                    raise ValueError('Invalid topic.')
                topic_qos_list.append((t[0].encode('utf-8'), t[1]))

        if topic_qos_list is None:
            raise ValueError("No topic specified, or incorrect topic type.")

        if self._sock is None and self._ssl is None:
            return (MQTT_ERR_NO_CONN, None)

        return self._send_subscribe(False, topic_qos_list)