ModuleNotFoundError: No module named 'launch'

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Running python3 rrbot_system_position_only.launch.pyfrom here https://github.com/ros-controls/ros2_.... But following the error message appears

Traceback (most recent call last):
  File "/home/ros2_control_demos/ros2_control_demo_bringup/launch/rrbot_system_position_only.launch.py", line 15, in <module>
    from launch import LaunchDescription
ModuleNotFoundError: No module named 'launch'

I already tried the solution suggested in https://answers.ros.org/question/3890... but that did not work. Can you guys please help me solve this error? Thank you.