code: def add_send_message(self, connection, send_message):
          
          self._send_message[connection] = send_message
          LOGGER.debug("Added send_message function "
                       "for connection %s", connection)
docs: Adds a send_message function to the Dispatcher's
          dictionary of functions indexed by connection.
  
          Args:
              connection (str): A locally unique identifier
                  provided by the receiver of messages.
              send_message (fn): The method that should be called
                  by the dispatcher to respond to messages which
                  arrive via connection.