[yarp] Add section on YARP with Python3

[jgvictores]

Some users have been struggling with YARP and Python3.

Here are some pointers to issues that may help for adding a section to the guide, or at least help for now:

• Most recent: Simple GUI to control camera parameters with YARP yarp-devices#145 (comment)
• YARP devel still not compiling with python bindings robotology/yarp#1341
• Python binding not compiling robotology/yarp#1024

[gsaponaro]

Hi @jgvictores , I was having an "outsider's view" on your guides. Pretty useful stuff, thank you. About this particular issue #26, I built YARP Python 3 bindings like this: robotology/yarp#1149 (comment)
My system has both Python 2 and Python 3. If I didn't do the above trick, YARP would give priority to Python 2.

[jgvictores]

Pretty useful stuff, thank you.

Thanks! We actually had a small debate at roboticslab-uc3m/questions-and-answers#3 before setting it up. I'm usually in favor of improving external projects rather than storing internal documents, but sometimes PRs are too slow, or we may want to do specific stuff like freeze at a certain version.

I built YARP Python 3 bindings like this: robotology/yarp#1149 (comment)

That's helpful and also reactivates the topic. :-)

I'm still bumping into something like this (CMAKE_INSTALL_PYTHONDIR is apparently ignored), which I've documented at 772afc4. I wanted to dive a bit more into the CMake before posting yet another issue on YARP, but feel free to open it, we could continue the conversation there if you consider it noteworthy.

Cheers!

[jgvictores]

PS: Issue not exactly the same, there there was a /usr vs /usr/local issue... and comment on PYTHON_INSTDIR vs CMAKE_INSTALL_PYTHONDIR; still similar.

[gsaponaro]

Sure, I'll be glad to help with YARP/Python/CMake tests. I'm not knowledgeable in SWIG though.

Not sure what kind of issue/patch should be proposed upstream at this moment. Feel free to tag me if you think of something. Ideally, on a system with the latest Ubuntu LTS (currently 16.04, soon 18.04) and both Python 2 and 3, I'd like to have the possibility of selecting between 2 and 3 in YARP CMake robustly.

[PeterBowman]

See robotology/community#391.

[PeterBowman]

YARP has moved on since 2017/18, now Python 3 is required and collisions between Python v2/v3 should no longer be a thing, if I'm correct. At least I managed to compile and use it successfully with just a tiny bit of hassle, properly reported and documented thereafter by myself at 7a9134f.

@jgvictores do you think that guide needs to expand a bit further on this matter, or is it good to go and you're fine for this issue to be closed?

[jgvictores]

Good to go, thank you all!