ModuleNotFoundError: No module named 'em' despite empy being installed when using colcon build in carla-ros-bridge wsl-2

Question

When running colcon build in the carla-ros-bridge root directory in wsl-2, python throws ModuleNotFoundError: No module named 'em'. Specifically, it produces this output:

--- stderr: carla_ros_scenario_runner_types
CMake Error at /opt/ros/foxy/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:60 (message):
  execute_process(/home/jakob/miniconda3/bin/python3 -m rosidl_adapter
  --package-name carla_ros_scenario_runner_types --arguments-file
  /home/jakob/carla-ros-bridge/build/carla_ros_scenario_runner_types/rosidl_adapter__arguments__carla_ros_scenario_runner_types.json
  --output-dir
  /home/jakob/carla-ros-bridge/build/carla_ros_scenario_runner_types/rosidl_adapter/carla_ros_scenario_runner_types
  --output-file
  /home/jakob/carla-ros-bridge/build/carla_ros_scenario_runner_types/rosidl_adapter/carla_ros_scenario_runner_types.idls)
  returned error code 1:

  Traceback (most recent call last):

    File "/home/jakob/miniconda3/lib/python3.10/runpy.py", line 196, in _run_module_as_main
      return _run_code(code, main_globals, None,
    File "/home/jakob/miniconda3/lib/python3.10/runpy.py", line 86, in _run_code
      exec(code, run_globals)
    File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_adapter/__main__.py", line 19, in <module>
      sys.exit(main())
    File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_adapter/main.py", line 53, in main
      abs_idl_file = convert_to_idl(
    File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_adapter/__init__.py", line 18, in convert_to_idl
      from rosidl_adapter.msg import convert_msg_to_idl
    File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_adapter/msg/__init__.py", line 16, in <module>
      from rosidl_adapter.resource import expand_template
    File "/opt/ros/foxy/lib/python3.8/site-packages/rosidl_adapter/resource/__init__.py", line 19, in <module>
      import em

  ModuleNotFoundError: No module named 'em'

Call Stack (most recent call first):
  /opt/ros/foxy/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:130 (rosidl_adapt_interfaces)
  CMakeLists.txt:39 (rosidl_generate_interfaces)


---

I've read elsewhere that this error is caused by the package "empy" missing, so I ran pip3 install empy and pip install empy, both produced the output: Defaulting to user installation because normal site-packages is not writeable Requirement already satisfied: empy in /home/jakob/.local/lib/python3.8/site-packages (3.3.4)

python -V outputs: Python 2.7.18 python3 -V outputs: Python 3.8.10

I'm running out of ideas to fix this

I tried: -Installing em and running the build again (throws different error message) -reinstalling empy (no changes) -removing the carla-ros-bridge root directory and cloning it again

Answer 1

I found the error. If you take a look at the Traceback, you'll see that Python uses two different paths to two different versions. Specifically /home/jakob/miniconda3/lib/python3.10/ and /opt/ros/foxy/lib/python3.8/site-packages/. This was due to me building ros foxy in a different miniconda environment than the carla-ros-bridge. The fix was deleting the carla ros bridge and downloading and then building it again in an environment that used python 3.8.