def _unsupportedVersionReceived(self, remoteVersion):
        """
        Called when an unsupported version of the ssh protocol is received from
        the remote endpoint.

        @param remoteVersion: remote ssh protocol version which is unsupported
            by us.
        @type remoteVersion: L{str}
        """
        self.sendDisconnect(DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED,
            b'bad version ' + remoteVersion)

        Called when an unsupported version of the ssh protocol is received from
        the remote endpoint.

        @param remoteVersion: remote ssh protocol version which is unsupported
            by us.
        @type remoteVersion: L{str}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/ssh/transport.py