Returns the usage string for this method.
        
        :return     <str>

def usage(self):
        """
        Returns the usage string for this method.
        
        :return     <str>
        """
        arg_list = ' '.join(self.cmd_args).upper()
        name = self.interface.name()
        return '%s [options] %s %s' % (name, self.__name__, arg_list)