code: def subscribe(self, topic, QoS, callback):
          
          return self._mqtt_core.subscribe(topic, QoS, callback)
docs: **Description**
  
          Subscribe to the desired topic and register a callback.
  
          **Syntax**
  
          .. code:: python
  
            # Subscribe to "myTopic" with QoS0 and register a callback
            myAWSIoTMQTTClient.subscribe("myTopic", 0, customCallback)
            # Subscribe to "myTopic/#" with QoS1 and register a callback
            myAWSIoTMQTTClient.subscribe("myTopic/#", 1, customCallback)
  
          **Parameters**
  
          *topic* - Topic name or filter to subscribe to.
  
          *QoS* - Quality of Service. Could be 0 or 1.
  
          *callback* - Function to be called when a new message for the subscribed topic
          comes in. Should be in form :code:`customCallback(client, userdata, message)`, where
          :code:`message` contains :code:`topic` and :code:`payload`. Note that :code:`client` and :code:`userdata` are
          here just to be aligned with the underneath Paho callback function signature. These fields are pending to be
          deprecated and should not be depended on.
  
          **Returns**
  
          True if the subscribe attempt succeeded. False if failed.