Called when the connection is lost or closed.

        The argument is either an exception object or None. The latter means
        a regular EOF is received, or the connection was aborted or closed by
        this side of the connection.

def connection_lost(self, exception):
        """Called when the connection is lost or closed.

        The argument is either an exception object or None. The latter means
        a regular EOF is received, or the connection was aborted or closed by
        this side of the connection.
        """
        if exception:
            self.logger.exception('Connection lost!')
        else:
            self.logger.info('Connection lost')