[robot_description]: no such command [[‘/opt/ros/noetic/share/xacro/xacro.py‘ 出错解决ros_noetic

环境: Ubuntu20.04 | ros版本Noetic
问题描述:
运行roscore时
也就是:roslaunch robot_sim_demo robot_spawn.launch
出现

RLException: while processing /home/lz/demo_ws/src/ROS-Academy-for-Beginners/robot_sim_demo/launch/include/xbot-u.launch.xml:
Invalid  tag: Cannot load command parameter [robot_description]: no such command [['/opt/ros/noetic/share/xacro/xacro.py', '/home/lz/demo_ws/src/ROS-Academy-for-Beginners/robot_sim_demo/urdf/robot.xacro']]. 

Param xml is 
The traceback for the exception was written to the log file

解决办法

vi ~/[你的工作空间 your workspace]/src/ROS-Academy-for-Beginners/robot_sim_demo/launch/include/xbot-u.launch.xml

修改

修改为

然后:wq退出
然后执行:

pip install defusedxml  
或者
pip3 install defusedxml

问题解决