ros自定义消息的时候报错ImportError: No module named em

Traceback (most recent call last):
  File "/opt/ros/kinetic/share/gencpp/cmake/../../../lib/gencpp/gen_cpp.py", line 41, in <module>
    import genmsg.template_tools
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/genmsg/template_tools.py", line 39, in <module>
    import em

ImportError: No module named em

python -m pip install empy

解决

sudo pip install empy用这个安装后还是不行的

没有细究两个有啥区别。