catkin_make errors with cmake regarding PY_em/PY_EM/empy/em

[trevoravant]

I am having the same error as this comment on the ros-melodic-catkin package's AUR page. Unfortunately, I have not been able to resolve it. I'm posting it here because the AUR page suggested opening issues on Github rather than as comments on the AUR page.

I installed ros-melodic-ros-base using yay: yay -S ros-melodic-ros-base. I wasn't able to install it using pikaur (see this issue) as was suggested by ROS's install instructions. The installation with yay took awhile but seemed to complete successfully.

I then completed the rest of the steps on the ROS install instructions page. Next, I tried doing the first ROS tutorial, but catkin_make gave me the following error:

$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/
$ catkin_make
Base path: /home/trevor/catkin_ws
Source space: /home/trevor/catkin_ws/src
Build space: /home/trevor/catkin_ws/build
Devel space: /home/trevor/catkin_ws/devel
Install space: /home/trevor/catkin_ws/install
Creating symlink "/home/trevor/catkin_ws/src/CMakeLists.txt" pointing to "/opt/ros/melodic/share/catkin/cmake/toplevel.cmake"
####
#### Running command: "cmake /home/trevor/catkin_ws/src -DCATKIN_DEVEL_PREFIX=/home/trevor/catkin_ws/devel -DCMAKE_INSTALL_PREFIX=/home/trevor/catkin_ws/install -G Unix Makefiles" in "/home/trevor/catkin_ws/build"
####
CMake Warning (dev) in CMakeLists.txt:
  No project() command is present.  The top-level CMakeLists.txt file must
  contain a literal, direct call to the project() command.  Add a line of
  code such as

    project(ProjectName)

  near the top of the file, but after cmake_minimum_required().

  CMake is pretending there is a "project(Project)" command on the first
  line.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- The C compiler identification is GNU 9.1.0
-- The CXX compiler identification is GNU 9.1.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Using CATKIN_DEVEL_PREFIX: /home/trevor/catkin_ws/devel
-- Using CMAKE_PREFIX_PATH: /opt/ros/melodic
-- This workspace overlays: /opt/ros/melodic
-- Found PythonInterp: /usr/bin/python2 (found suitable version "2.7.16", minimum required is "2") 
-- Using PYTHON_EXECUTABLE: /usr/bin/python2
-- Using default Python package layout
-- Could NOT find PY_em (missing: PY_EM) 
CMake Error at /opt/ros/melodic/share/catkin/cmake/empy.cmake:29 (message):
  Unable to find either executable 'empy' or Python module 'em'...  try
  installing the package 'python-empy'
Call Stack (most recent call first):
  /opt/ros/melodic/share/catkin/cmake/all.cmake:163 (include)
  /opt/ros/melodic/share/catkin/cmake/catkinConfig.cmake:20 (include)
  CMakeLists.txt:56 (find_package)


-- Configuring incomplete, errors occurred!
See also "/home/trevor/catkin_ws/build/CMakeFiles/CMakeOutput.log".
Invoking "cmake" failed

Here is the CMakeOutput.log file: CMakeOutput.log

Any help would be appreciated.

Thanks

[bionade24]

You ran in the empy executable problem, which isn't a problem of our packaging. You should ask such questions on https://aswers.ros.org, instead of here (It's already answered there). But you could ask me if you want on freenode, mail or elsewhere, too.
Solution: If you want to use python2, install python2-empy, otherwise you have to tell cmake to use python3.

[acxz]

Since I had also ran into this issue ros-melodic-arch/ros-melodic-ros-base#2. I decided to edit the ROS Tutorial Page so that the information on building catkin workspaces in somewhere more visible.

[seth814]

In my case, catkin was looking at my python version installed in anaconda.
I just catkin make -DPYTHON_EXECUTABLE=/usr/bin/python3 like it says on the page acxz posted.
Install was able to find python3-empy now and continue.

[bionade24]

In my case, catkin was looking at my python version installed in anaconda.
I just catkin make -DPYTHON_EXECUTABLE=/usr/bin/python3 like it says on the page acxz posted.
Install was able to find python3-empy now and continue.

Yes, that's necessary and also covered in Arch Wiki.