Multirelease effort: Moving to Python 3

[Bohuslav Kabrda]

Hi all,
as a new Fedora Python maintainer, I have set myself a goal of moving Fedora to Python 3 as a default. This is going to be a multirelease effort that is going to affect lots of Fedora parts. Since we will need to switch default package manager from Yum to DNF (which is supposed to work with Python 3), we will need to wait for that. I've been told that DNF should be default in F22, so that's my target, too. That should also give everyone else plenty of time to work on other essential packages to make this happen.

Here is my analysis/proposal:
Before switching, we need to make sure that everything "important" (*) is Python 3 compatible. There are three steps I see in this transition:
1) Getting rid of Python 2 in mock minimal buildroot.
2) Porting Anaconda to Python 3.
3) Making all livecd packages depend on Python 3 by default (and eventually getting rid of Python 2 from livecd) - this will also require switching from Yum to DNF as a default, that is supposed to support Python 3.
( 4) Making as much of the remaining packages Python 3 compatible )

In past few days, I've been going through packages that are part of the above steps. I have reported numerous bugs asking upstream and/or Fedora maintainers for help with porting to Python 3. We have some spare cycles in our small Python packaging team, that we will try to provide to whoever needs them most, but we're limited and we'll have to rely on the upstreams to do most of the work. I'm attaching a document with list of packages that need porting with some notes/links to opened bugs. Sometime soon, I'll open a tracking bug for this, so that everyone can see where we are quickly.
(*) I call these "important" packages (in terms of being important for the Python 3 switch)

>From packaging point of view, this will probably require:
1) Renaming python package to python2
2) Renaming python3 package to python
3) Switching the %{?with_python3} conditionals in specfiles to %{?with_python2} (we will probably create a script to automate this, at least partially)


FAQ:
Q: Why do we need to switch to Python 3?
A: Because Python 2 is old, slower, less pythonic, doesn't get any more functionality and it won't be that long before the official upstream support ends [1]

Q: How do I port to Python 3?
A: There are tons of tutorials and howtos about porting and the differencies in general. E.g. [2] (general), [3] (c-extensions)

Q: What about Python 2?
A: We will maintain that at least as long as upstream supports it. After that, I'd prefer dropping it, but since I know there will be people wanting to keep it around, I'll gladly give the maintenance to someone else.


I'll be glad to answer all your questions and discuss the above points. Nothing is set into stone and I'd love to hear your ideas and comments.
Thanks for reading this through!
Slavek.

-- 
Regards,
Bohuslav "Slavek" Kabrda.

[1] http://www.python.org/dev/peps/pep-0373/
[2] http://docs.python.org/dev/howto/pyporting.html
[3] http://docs.python.org/3/howto/cporting.html
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