Port the code to python3 and/or python2-3 compatible code

[jorgejesus]

Current code is only python2 compatible.

Possibility:

• Change code to python3 and only use python3
• Change code to be python2.7 and python3.3 compatible
• PyPy ??? (https://pypy.org/) (this could be hard)

Tools/Docs:
http://python-future.org/
Testing different possibility with tox:
https://tox.readthedocs.io/en/latest/

[jorgejesus]

Extra docs and explanation how to processed with extra tools
https://docs.python.org/3/howto/pyporting.html

[justb4]

Welcomed. I just did the reverse: Python3 project also supporting Py2: schettino72/sqla_yaml_fixtures#1 what especially helped is more thorough tests, CI and code coverage (even went to 100% code coverage, but ok small project). GHC has some tests now but not exhaustive, so we should work on that as well to make the transition smoother.

[tomkralidis]

Update: following discussion on Gitter, given the 0.6.0 release we will update master to be Python 3 only moving forward.

[justb4]

@tomkralidis @borrob @jorgejesus
Like many projects as Django (2.0 is PY3 only) etc, I would prefer not to have simultaneous Py2 and Py3 support, given that:

• Py2 will be EOL very soon (less than a year)
• maintenance: we already have limited human resources
• many users (more and more) are deploying with Docker

Like with Stetl in a similar PR we decided to:

• bring out one last Py2 release (and Docker Image)
• make a branch of that release, for urgent fixes only
• bring out fresh Py3-only version

[borrob]

I'm working on the conversion to python3 (but somehow I can't assign this task to myself). I'm using the version that comes standard with buster (I believe that is 3.7.2), but so far I think any '3' version will do.

I am aiming for a py3-only version, so as to keep the code as clean and simple as possible.

[tomkralidis]

I've added you as a collaborator so you should be able to assign yourself now - can you let me know if it works?

Agree, py3-only version. We can cut a last released for Python 2 support when ready to merge the Python 3 work.