编译出现问题：
python import error: No module named ‘em’
Required python packages not installed.
On a Debian/Ubuntu system please run:
sudo apt-get install python-empy
sudo pip install catkin_pkg
On MacOS please run:
sudo pip install empy catkin_pkg
On Windows please run:
easy_install empy catkin_pkg
方法：
链接：https://blog.csdn.net/sinat_21190681/article/details/83508442
运行
python -m pip install empy
问题消失
