ros运行catkin_make报警：No module named em......

问题描述

在跟着ros教程学习“创建ros消息和ros服务”(http://wiki.ros.org/cn/ROS/Tutorials/CreatingMsgAndSrv)时：添加了msg和srv之后，在终端中执行catkin_make命令报错了，编译失败的原因首先是ModuleNotFoundError: 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
ModuleNotFoundError: No module named 'em'
beginner_tutorials/CMakeFiles/beginner_tutorials_generate_messages_cpp.dir/build.make:63: recipe for target '/home/skipper/catkin_ws/devel/include/beginner_tutorials/Num.h' failed
make[2]: *** [/home/skipper/catkin_ws/devel/include/beginner_tutorials/Num.h] Error 1
CMakeFiles/Makefile2:1192: recipe for target 'beginner_tutorials/CMakeFiles/beginner_tutorials_generate_messages_cpp.dir/all' failed
make[1]: *** [beginner_tutorials/CMakeFiles/beginner_tutorials_generate_messages_cpp.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

寻找了许多解决方法例如执行命令python -m pip install empy、pip install em，仍然不能直接解决问题。

$ python -m pip install empy
/home/skipper/.local/lib/python2.7/site-packages/pip/_vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
  warnings.warn(warning, RequestsDependencyWarning)
DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7. More details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
Requirement already satisfied: empy in /usr/lib/python2.7/dist-packages (3.3.2)

我的解决方法

运行了python -m pip install empy命令后，发现empy是成功地安装在了/usr/lib/python2.7/dist-packages中，而不是编译时报错的**/opt/ros/kinetic/lib/python2.7/dist-packages**中，因此尝试是否可以将empy.py文件从/usr复制到/ros中去：

sudo cp /usr/lib/python2.7/dist-packages/em.py /opt/ros/kinetic/lib/python2.7/dist-packages/

然后重新打开一个终端，在工作空间中再次执行catkin_make命令，发现编译成功：

skipper@ren9000:~/catkin_ws$ catkin_make
Base path: /home/skipper/catkin_ws
Source space: /home/skipper/catkin_ws/src
Build space: /home/skipper/catkin_ws/build
Devel space: /home/skipper/catkin_ws/devel
Install space: /home/skipper/catkin_ws/install
####
#### Running command: "make cmake_check_build_system" in "/home/skipper/catkin_ws/build"
####
####
#### Running command: "make -j8 -l8" in "/home/skipper/catkin_ws/build"
####
[  0%] Built target std_msgs_generate_messages_py
[  0%] Built target std_msgs_generate_messages_nodejs
[  0%] Built target std_msgs_generate_messages_eus
[  0%] Built target std_msgs_generate_messages_lisp
[  0%] Built target std_msgs_generate_messages_cpp
[  0%] Built target _beginner_tutorials_generate_messages_check_deps_AddTwoInts
[  0%] Built target _beginner_tutorials_generate_messages_check_deps_Num
[ 53%] Generating C++ code from beginner_tutorials/AddTwoInts.srv
[ 38%] Built target beginner_tutorials_generate_messages_lisp
[ 38%] Generating C++ code from beginner_tutorials/Num.msg
[ 61%] Built target beginner_tutorials_generate_messages_eus
[ 84%] Built target beginner_tutorials_generate_messages_py
[100%] Built target beginner_tutorials_generate_messages_nodejs
[100%] Built target beginner_tutorials_generate_messages_cpp
Scanning dependencies of target beginner_tutorials_generate_messages
[100%] Built target beginner_tutorials_generate_messages

待续

这个只是我的解决方法，至于这样直接复制有没有问题，还不知道——可能只能解决了编译问题，不能解决潜在的其他问题。

参考链接

ros自定义消息的时候报错ImportError: No module named em
https://blog.csdn.net/wawayu_0/article/details/79460043