First Python 3 only release

[ejeschke]

Ginga is currently Python 2/3 compatible. At some point Ginga will switch to a Python 3 only code base. The only question is when, and how.

One idea would be to follow the astropy lead and designate the Ginga 2.x releases as the last Python 2 compatible versions. Releases from Ginga 3.0 onward will be Python 3.6+ compatible only. Personally, I like this scheme as it also matches the Python versioning somewhat and therefore may be intuitive to developers and users.

This issue is to simply set up discussion around a plan.

[ejeschke]

@pllim, is there a schedule for making astropy-helpers python 3 only?

[ejeschke]

Ending Py2Py3 compatibility in a user friendly manner PyCon 2017.

[pllim]

I believe astropy-helpers that goes with astropy 3.0 is already PY3 only but @bsipocz can confirm.

[pllim]

Releases from Ginga 3.0 onward will be Python 3.6+ compatible only

That sounds sensible. However, if you have plans to support Ginga 2.x bug fixes after 3.0 release, you might need to branch off 2.x and do backports, similar to Astropy. Just a thought.

[ejeschke]

you might need to branch off 2.x and do backports

That was my thought also. That seems reasonable.

[bsipocz]

we made the decision to have astropy-helpers 3.0 python3 only along with the core package, but provide backports 2.0.x whenever possible (including some of the new "features" too when possible and when they don't break compatibility).