python API for roslaunch with parameter

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I want to run a roslaunch file with parameter, I follow this tutorial:

import roslaunch
uuid = roslaunch.rlutil.get_or_generate_uuid(None, False)
cli_args = ['/home/m/catkin_ws/src/rl_nav/launch/nav_gazebo.launch','maze_id:=2']
roslaunch_args = cli_args[1:]
roslaunch_file = [(roslaunch.rlutil.resolve_launch_arguments(cli_args)[0], roslaunch_args)]
parent = roslaunch.parent.ROSLaunchParent(uuid, roslaunch_file)
parent.start()

But when I run this script, there is an error:

TypeError: not all arguments converted during string formatting

Why does it and how can I solve it? Thank you.