How to fix this python's roslaunch API error?

edit

I follow this procedure to execute roslaunch file with argument via python like this:

    # launch recording program
    uuid = roslaunch.rlutil.get_or_generate_uuid(None, False)
    roslaunch.configure_logging(uuid)
    cli_args = [
        'hw_interface',
        'main.launch',
        'save_path:=/mnt/usb-SanDisk_Ultra_Fit_4C530001151128104110-0:0-part1'
    ]
    roslaunch_file = roslaunch.rlutil.resolve_launch_arguments(cli_args)
    roslaunch_args = cli_args[2:]
    launch_file = [(roslaunch_file, roslaunch_args)]
    parent = roslaunch.parent.ROSLaunchParent(uuid, launch_file)
    parent.start()

But it returns this error:

File "/opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/config.py", line 450, in load_config_default
    logger.info('loading config file %s'%f)
TypeError: not all arguments converted during string formatting

similar question has been asked here but still no answer.