Python3 compatibility

[hgaiser]

Hey,

As is my understanding, ROS packages should aim to be python2 and python3 compatible. Currently on my system cv_bridge is linking against libboost_python.so though, which causes an issue for me since I am using a python3 interpreter and libboost_python.so is for python2 bindings (libboost_python3.so is for python3 bindings). The issue seems to come from this line, which should be find_package(Boost REQUIRED python3) in my case.

However simply changing this to python3 will break python2 compatibility. Perhaps some option should be added to the CMakeLists.txt for choosing python3/python2.

Best regards,
Hans

[vrabaud]

So, I solved it by checking which version of Python is installed. Now, as you mentioned, there should probably something at the level of CMake: what if you have Python2 installed and want to build for Python 3 ? (not sure we want to support that),

[hgaiser]

Yes I agree it would be better to have a boolean to determine if you want to compile with Python 2 or 3. I'm thinking it'd be better if it was a catkin flag, which is passed down to cmake. That way there'd be a ROS-wide flag of determining to compile with Python 2/3.

[hdamron17]

Would it be possible to compile the version dependent part for both python 2 and 3 then use six to determine at runtime which to import?