cannot launch under ros2 foxy

[electop]

Environment

• OS: Ubuntu 20.04.04 LTS
• ROS version: ROS2 Foxy

Error Message

[INFO] [launch]: All log files can be found below /home/electop/.ros/log/2021-10-23-07-51-49-750505-NT950-131680
[INFO] [launch]: Default logging verbosity is set to INFO
Task exception was never retrieved
future: <Task finished name='Task-2' coro=<LaunchService._process_one_event() done, defined at /opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py:226> exception=InvalidLaunchFileError('py')>
Traceback (most recent call last):
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/any_launch_file_utilities.py", line 53, in get_launch_description_from_any_launch_file
    return loader(launch_file_path)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/python_launch_file_utilities.py", line 62, in get_launch_description_from_python_launch_file
    launch_file_module = load_python_launch_file_as_module(python_launch_file_path)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/python_launch_file_utilities.py", line 37, in load_python_launch_file_as_module
    loader.exec_module(mod)
  File "<frozen importlib._bootstrap_external>", line 848, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/electop/robot_ws/install/marvelmind_nav/share/marvelmind_nav/launch/marvel_driver_launch.py", line 14, in <module>
    from launch_ros import get_default_launch_description
ImportError: cannot import name 'get_default_launch_description' from 'launch_ros' (/opt/ros/foxy/lib/python3.8/site-packages/launch_ros/__init__.py)

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py", line 228, in _process_one_event
    await self.__process_event(next_event)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py", line 248, in __process_event
    visit_all_entities_and_collect_futures(entity, self.__context))
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures
    futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures
    futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 38, in visit_all_entities_and_collect_futures
    sub_entities = entity.visit(context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/action.py", line 108, in visit
    return self.execute(context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/actions/include_launch_description.py", line 125, in execute
    launch_description = self.__launch_description_source.get_launch_description(context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_source.py", line 84, in get_launch_description
    self._get_launch_description(self.__expanded_location)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/any_launch_description_source.py", line 53, in _get_launch_description
    return get_launch_description_from_any_launch_file(location)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_description_sources/any_launch_file_utilities.py", line 56, in get_launch_description_from_any_launch_file
    raise InvalidLaunchFileError(extension, likely_errors=exceptions)
launch.invalid_launch_file_error.InvalidLaunchFileError: Caught exception when trying to load file of format [py]: cannot import name 'get_default_launch_description' from 'launch_ros' (/opt/ros/foxy/lib/python3.8/site-packages/launch_ros/__init__.py)

[ipa-kut]

Thank @electop for pointing out this issue. I ported this into ROS2 back in Dashing and have not tested it since then. I am not sure when/if I will be able to tackle this though, but I will try. If you make a PR for this, I would really welcome it!