Switch to python 3

[basicNew]

This requires latest Drake, so goes hand-in-hand with maliput/delphyne_gui#179

Steps to migrate:

• Use delphyne's gui PR to bring latest Drake.
• Change a bit the way we prepare to build drake (note the last script):

mkdir -p delphyne_ws/src
cd delphyne_ws
# Bootstrap the workspace
sudo apt install git
git clone git@github.com:ToyotaResearchInstitute/delphyne-gui.git src/delphyne_gui
# Install a few tools to setup the rest of the workspace
sudo ./src/delphyne_gui/tools/install_prereqs.sh
# Clone the remaining source repositories into the workspace
vcs import src < src/delphyne_gui/delphyne.repos
# Additionally retrieve drake system dependencies
sudo ./src/drake/setup/ubuntu/18.04/install_prereqs.sh
# Setup platform
./src/drake/setup/ubuntu/source_distribution/install_prereqs_user_environment.sh

• Change a bit the way we build drake (note the --config=python3 flag):

cd delphyne_ws
# Drake
pushd src/drake
bazel run --config=python3 //:install `pwd`/../../install
popd

• Make sure your $PYTHONPATH points to a 3.6 install and not a 2.7

All the demos should run and the tests should pass.

@clalancette @hidmic haven't yet checked on CI, wanted to push this as soon as I got it so you could confirm this is working locally too

[clalancette]

I tried this out, and it worked! I ended up having two problems:

1. I had to completely remove delphyne_ws/install and build/delphyne for it to build properly.
2. I had to update delphyne_gui/setup.bash to point to the python3 stuff.

Otherwise, I ran all of the demos and they all seemed to work pretty well. This is awesome @basicNew !

[basicNew]

@clalancette thanks for checking this so quickly! Indeed, I forgot to mention I nuked build and install before this, sorry about that. And thanks for pointing out about delphyne_gui/setup.bash, I'll update the PR to include that.

[basicNew]

Alright, CI is passing! @hidmic would you mind testing this one (check @clalancette 's comments)? If everything goes ok I think we could merge this one.

[clalancette]

I left a couple of small nits in the code that is here.

However, I think we need to change a bit more of the CI code. In particular I think we need to remove https://github.com/ToyotaResearchInstitute/delphyne-gui/blob/master/tools/install_prereqs.sh#L43, change https://github.com/ToyotaResearchInstitute/delphyne-gui/blob/master/tools/install_prereqs.sh#L80 to python3, etc. Also, I'm surprised that we didn't have to change the name of the tarball that we fetch: https://github.com/ToyotaResearchInstitute/delphyne/blob/master/tools/continuous_integration/jenkins/build#L20 ; is python3 bindings automatically included in the "default" nightly tarballs now?

[clalancette]

I don't feel strongly about adding this, but I'm surprised you needed it, given that we only support Linux at the moment.

[basicNew]

yup, I was surprised require this too, but otherwise the characters used from ignition logging (spaces and colors) were all escaped and output was a mess.

[clalancette]

Ah, I see. Good reason to use it then; I'll just suggest that you put a comment in there saying that we need it for that reason.

[hidmic]

Comments added!

[clalancette]

The fact that you didn't have to change this to python3-pip suggests that we don't actually need pip anymore; I'd suggest removing this.

[basicNew]

+1, I'll take a shot at it

[hidmic]

Working fine on my end, LGTM pending @clalancette comments' resolution!

[hidmic]

@clalancette

In particular I think we need to remove...

Done!

Also, I'm surprised that we didn't have to change the name of the tarball that we fetch

AFAIK nightly include python3 support, see relevant comment here.

[hidmic]

Let's see what CI has to say.

[hidmic]

@clalancette @basicNew looks like CI is happy :)