def loseConnection(self, connDone=failure.Failure(main.CONNECTION_DONE)):
        """
        Stop accepting connections on this port.

        This will shut down the socket and call self.connectionLost().  It
        returns a deferred which will fire successfully when the port is
        actually closed, or with a failure if an error occurs shutting down.
        """
        self.disconnecting = True
        self.stopReading()
        if self.connected:
            self.deferred = deferLater(
                self.reactor, 0, self.connectionLost, connDone)
            return self.deferred

        Stop accepting connections on this port.

        This will shut down the socket and call self.connectionLost().  It
        returns a deferred which will fire successfully when the port is
        actually closed, or with a failure if an error occurs shutting down.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/tcp.py