def extendedRequest(extendedName, extendedData):
        """
        This is the extension mechanism for SFTP.  The other side can send us
        arbitrary requests.

        If we don't implement the request given by extendedName, raise
        NotImplementedError.

        The return value is a string, or a Deferred that will be called
        back with a string.

        @param extendedName: the name of the request as a string.
        @param extendedData: the data the other side sent with the request,
        as a string.
        """

        This is the extension mechanism for SFTP.  The other side can send us
        arbitrary requests.

        If we don't implement the request given by extendedName, raise
        NotImplementedError.

        The return value is a string, or a Deferred that will be called
        back with a string.

        @param extendedName: the name of the request as a string.
        @param extendedData: the data the other side sent with the request,
        as a string.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/interfaces.py