crazyflie-interfaces build issue and Empy 4.0.0 incompatible

[knmcguire]

I've just did a fresh install of crazyswarm2 on my 24.04 so I'll make an issue of those that are still current.

When installing, usually empy needs to be installed as well with pip3 install empy lark catkin-pkg which is currently missing from our documentation. This is necessary for building the crazyflie_interfaces (rosidl).

However, there is currently an incompatibility with Empy 4.0.0 which causes these two errors:

...
    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/resource/__init__.py", line 51, in evaluate_template
      em.BUFFERED_OPT: True,
      ^^^^^^^^^^^^^^^

  AttributeError: module 'em' has no attribute 'BUFFERED_OPT'

...

    File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/resource/__init__.py", line 69, in evaluate_template
      _interpreter.shutdown()
      ^^^^^^^^^^^^^^^^^^^^^

  AttributeError: 'NoneType' object has no attribute 'shutdown'

solution

This is due to this error: ros2/rosidl#779

Downgrade empy to:

pip3 install empy==3.3.4