code: def set_extana_callback(self, callback, data=None):
          
          self.extana_callback = callback
          self.extana_callback_data = data
docs: Register a callback for incoming data packets from the SK8-ExtAna board.
  
          This method allows you to pass in a callable which will be called on 
          receipt of each packet sent from the SK8-ExtAna board. Set to `None` to
          disable it again.
  
          Args:
              callback: a callable with the following signature:
                          (ana1, ana2, temp, seq, timestamp, data)
                        where:
                          ana1, ana2 = current values of the two analogue inputs
                          temp = temperature sensor reading
                          seq = packet sequence number (int, 0-255)
                          timestamp = value of time.time() when packet received
                          data = value of `data` parameter passed to this method
              data: an optional arbitrary object that will be passed as a 
                  parameter to the callback