[Scons-users] How important is python 3?

[Evan Driscoll]

[TL;DR version at the end]

I think it won't be too long now until distros will start switching to 
Python 3 by default. (By "default" I mostly mean which version does 
"python" run, but to a lesser extent also what package you will get if 
you say "package-manager install python".) Ubuntu had a goal of only 
shipping Python 3 on their installation CDs for the latest release 
(12.10); I am not sure if they achieved it or not. They have a goal of 
moving Python 2 out of the main repository and into universe for 14.04 
(April '14). Arch moved to Python 3 by default in both senses over two 
years ago. Once that happens, the bar for using SCons gets raised. Maybe 
not by a lot for a bit, but it does go up by a little. (Especially for 
people who are using the site-specific version so that theoretically 
users don't have to install anything.)

I think a critical point was missed in your original question, which was 
whether the suggestion is to move to a code base that works with either 
2 or 3 (either by supporting both versions or with six or with 2to3 or 
3to2) or a pure Python 3 code base.

Also with regard to what version of Python 2 should be supported, in the 
past I've said that it wouldn't surprise me if a far number of people 
were using SCons with Python 2.4 because of RHEL 5. Full support 
(production phase 1) for RHEL 5 is apparently ending nowish ("Q4 2012"), 
so that is probably rapidly becoming less of an issue, if it ever was 
one in the first place. RHEL 6 ships with 2.6 by default, so I'm not 
sure how much that recommends against requiring 2.7. We use RHEL in my 
environment, but we also have lots of Python versions available.


So my votes:

* It's very possible the installation procedure already does this (I 
don't have a Python-3-by-default system to test on), but it seems like 
soon you'll have to change the shebang line to call "python2" instead of 
"python".

* With a mixed code base that supports both Python 2.6/2.7 and Python 
3.x, I vote +1.25. I think the Python 3 transition "has to" happen 
sometime in the next, I dunno, 2 or 3 years or SCons will really start 
to suffer, and it's definitely not premature to make the switch now.

* With a mixed code base that supports Python 2.7 and Python 3.x (but no 
2.6), I vote +1. A small amount of extra work for me I think.

* With a Python 3-only code base, I vote -1;  with most distros still on 
Python 2 by default, *this* does seem quite premature.


Evan