Run Python 3 Packages in Python 2 Workspace¶

The cv_bridge Issue¶

In the default setting the workspace is only built using Python 2. Also usually ROS supports only one Python version at a time. On the one hand we need python 2 for tools like rqt, but on the other hand software like the vision needs Python 3. If we want to build the cv_bridge which is needed for the Vision also in Python 3 we need to follow the following steps.

Execute the following commands to add another workspace beside your main one:

mkdir ~/secondary_build_ws && cd ~/secondary_build_ws && catkin config -DPYTHON_EXECUTABLE=/usr/bin/python3 -DPYTHON_INCLUDE_DIR=/usr/include/python3.6m -DPYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.6m.so && catkin config --install

Now we clone the OpenCv ros interface:

mkdir src && cd src && git clone -b melodic https://github.com/ros-perception/vision_opencv.git

We build the cv_bridge by running : catkin build cv_bridge. Dont worry about the failing tests.
In the last step we source the workspace beside the old workspace using: --extend.
- For Bash users:
  
  Best practice is to add the sourcing to the .bashrc by adding source ~/secondary_build_ws/devel/setup.sh --extend after sourcing of the primary workspace.
- For Zsh users:
  
  Best practice is to add the sourcing to the .bashrc by adding source ~/secondary_build_ws/devel/setup.zsh --extend after sourcing of the primary workspace.

The tf2 Issue¶

In addition to the cv_bridge we may also want to build tf2 for Python 3. The solution is similar to the cv_bridge approach. Instead of OpenCv clone clone https://github.com/ros/geometry2.git and build it with: catkin build tf2.