File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/resource/__init__.py", line 48, in evaluate_template _interpreter = em.Interpreter( AttributeError: module 'em' has no attribute 'Interpreter'

[ct2034]

When following the setup instructions, https://pyrobosim.readthedocs.io/en/latest/setup.html and first setup the venv, then run colcon build I end up with this error:

console output

``` CMake Error at /opt/ros/humble/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:59 (message): execute_process(/home/hec2le/python-virtualenvs/pyrobosim/bin/python3 -m rosidl_adapter --package-name pyrobosim_msgs --arguments-file /home/hec2le/ros/delib_ws/build/pyrobosim_msgs/rosidl_adapter__arguments__pyrobosim_msgs.json --output-dir /home/hec2le/ros/delib_ws/build/pyrobosim_msgs/rosidl_adapter/pyrobosim_msgs --output-file /home/hec2le/ros/delib_ws/build/pyrobosim_msgs/rosidl_adapter/pyrobosim_msgs.idls) returned error code 1: AttributeError processing template 'msg.idl.em' Traceback (most recent call last): File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/resource/__init__.py", line 48, in evaluate_template _interpreter = em.Interpreter( AttributeError: module 'em' has no attribute 'Interpreter' During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main return _run_code(code, main_globals, None, File "/usr/lib/python3.10/runpy.py", line 86, in _run_code exec(code, run_globals) File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/__main__.py", line 19, in sys.exit(main()) File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/main.py", line 53, in main abs_idl_file = convert_to_idl( File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/__init__.py", line 19, in convert_to_idl return convert_msg_to_idl( File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/msg/__init__.py", line 39, in convert_msg_to_idl expand_template('msg.idl.em', data, output_file, encoding='iso-8859-1') File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/resource/__init__.py", line 23, in expand_template content = evaluate_template(template_name, data) File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/resource/__init__.py", line 69, in evaluate_template _interpreter.shutdown() AttributeError: 'NoneType' object has no attribute 'shutdown' Call Stack (most recent call first): /opt/ros/humble/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:130 (rosidl_adapt_interfaces) CMakeLists.txt:37 (rosidl_generate_interfaces) ```

I was able to get around this by first building the workspace without venv. Recurrent build are okay with the venv.

Tested under humble / python 3.10

[sea-bass]

Yeah, this is an annoying one...

it works if you first activate the venv and THEN do source /opt/ros/humble/setup.bash before building.

The convenience script attempts to do this in being able to call source setup/source_pyrobosim.bash humble.

Let me better document that in the local setup...

[sea-bass]

Actually, I'm now noticing that is not enough. It has to do specifically with the EmPy<4 requirement that ROS enforces.

Can you try installing pip3 install colcon_common_extensions in the venv to see if that works for you? If it does, I can figure out some updates.

[ct2034]

No, got the same behavior. Pip installed EmPy==3.3.4. But the behavior is the same

[sea-bass]

I see... let's try something else. Could you:

1. Check out this branch
2. Set up with source setup/create_python_env.bash ros (the extra ros arg)
3. source setup/source_pyrobosim.bash humble
4. colcon build

Let me know...

[ct2034]

Sorry I am running out of time. But this did not work:

ERROR: Invalid requirement: './pyrobosim'
Hint: It looks like a path. File './pyrobosim' does not exist.
ERROR: Could not open requirements file: [Errno 2] No such file or directory: 'test/python_test_requirements.txt'
bash: [: missing `]'

[ct2034]

Why do you need this venv? It makes it all a bit complicated to handle. ;)

[sea-bass]

Yeah, I was running out of time myself. Will revisit this a bit later and make those scripts a little friendlier... but I think I understand the issue.

Sadly, it being first a standalone package and secondly a ROS wrapper creates these sorts of problems.

[sea-bass]

Why do you need this venv? It makes it all a bit complicated to handle. ;)

venvs are not needed, but they provide isolation. And in Ubuntu 24.04 you can't install directly into system Python, so we all have to move towards virtual envs or similar.

[ct2034]

for python packages, yes. But they really don't play nicely with ros

[sea-bass]

They indeed do not...

There is a related issue here to try address it by separating packages out. https://github.com/sea-bass/pyrobosim/issues/176

The idea would be to add pyrobosim to rosdep and have the ROS wrapper package simply depend on it as a binary install.

Would be nice to do, but I definitely will need help to figure that out.

[sea-bass]

@ct2034 I just took a more thorough pass at this problem and improved the setup scripts in https://github.com/sea-bass/pyrobosim/pull/183

I agree with you that the "right" thing for a ROS package is to make this work without virtual environments, but this is going to a big sweeping change that I am not able to do in the short term... nor do I want to necessarily make the ROS experience the primary goal of this package.