Support Python 3

[denisalevi]

TODOs that come to mind right now:

• Turn implicit to explicit imports
• from __future__ import division, print_function, absolte_import and replace integer division in code with '//'

[denisalevi]

@moritzaugustin @mstimberg Thinking to release brian2CUDA without Python2 support. What do you think? I suppose many people will stick with deprecated Python2 for a while. Could leave the transition to Python3 to just before the release and have one Python2 compatible version (with the current brian2 release which is the last supporting Python2), but then there would be certainly bugs to be fixed for the Python2 version. So I think I would prefer cleaning up the code now and transitioning to Python3 for good. Comments?

[thesamovar]

The last release of brian2 (2.3) will be the last with Python 2 support, and indeed we've just removed all Python 2 support from master, so I think it makes sense to only support Python 3.

[mstimberg]

Yep, I agree that going Python 3-only (>=3.6) makes a lot of sense for Brian2CUDA.

[denisalevi]

Great, will do so. Thanks for the comments. And @mstimberg why Python >= 3.6? Why not e.g. >= 3.5? (just out of curiosity)

[mstimberg]

And @mstimberg why Python >= 3.6? Why not e.g. >= 3.5? (just out of curiosity)

We'll only support versions >=3.6 with the next release of Brian, mostly because 3.6 offers a number of features that we want to use (f-strings, for example), but also simply because 3.5 will reach its end-of-life in September this year.

[denisalevi]

Brian2 PR that removes Python 2 support: brian-team/brian2#1147

[denisalevi]

And previous brian2 PR which uses Python 3 comaptible Python 2 code: brian-team/brian2#1073

[denisalevi]

And here is another PR, adding Python 3.8 compatibility: brian-team/brian2#1132

[denisalevi]

Implemented in PR #236. Closing.