def readConnectionLost():
        """
        Notification of the read connection being closed.

        This indicates peer did half-close of write side. It is now
        the responsibility of the this protocol to call
        loseConnection().  In addition, the protocol MUST make sure a
        reference to it still exists (i.e. by doing a callLater with
        one of its methods, etc.)  as the reactor will only have a
        reference to it if it is writing.

        If the protocol does not do so, it might get garbage collected
        without the connectionLost method ever being called.
        """

        Notification of the read connection being closed.

        This indicates peer did half-close of write side. It is now
        the responsibility of the this protocol to call
        loseConnection().  In addition, the protocol MUST make sure a
        reference to it still exists (i.e. by doing a callLater with
        one of its methods, etc.)  as the reactor will only have a
        reference to it if it is writing.

        If the protocol does not do so, it might get garbage collected
        without the connectionLost method ever being called.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/interfaces.py