Python 2/3 packaging

[Bohuslav Kabrda]

Hi everyone,

I've been thinking a lot about the whole concept of Python2/3 packaging and from my point of view it seems somehow confusing (renaming of python 3 binaries, split srpms/one srpm stuff and so on). I'm currently working with few people on a "stack" (or software collection) concept, that we are testing with Ruby and some of its libraries, as we are stepping to 1.9.3 from 1.8.7. Basically, the stack allows you to have one runtime (say, python2) in normal directory structure and then have a separate directory structure for another runtime (python3 in this case) under /opt. So you don't need to rename all paths and executables to python3-* and /usr/lib/python{2,3} or something like that, but instead you use
$ python-binary

for the core system executable and you run

$ scl enable python3 "python-binary"

(where python3 is the name of the stack).

A great advantage of this concept is, that you have only one specfile, which can be built both for the core system and for the stack and you don't need to do any renaming or stuff like that. So when you decide that python 3 should be in the core system, you just rebuild the packages in a different buildroot (I think it can be achieved for both the split python2/3 SRPMS and SRPMS which generate python2/3 RPMS from one source, but I'd have to think about a way how to do it nice and systematically for both cases - but split SRPMS would be better).
I'll try to explain how to get stack or core system RPM from one SRPM in different buildroots:
- There is a library called scl-utils [1], that is aimed at providing the core functionality for any stack. It has a runtime part, (the "scl enable ...") which takes care of redefining systems paths, and a build part, which contains redefinition of all macros that you normally use in the specfile (like %{_libdir} etc.).
- If the build part of scl-utils is present in the buildroot that you are building in, the resulting RPM has the relocated paths and installs under /opt. If the build part of scl-utils is not in the buildroot, the resulting RPM gets built normally for the core system.
(It is a little bit more complicated, but I think that everyone gets the point.)

If anyone of you is interested how this works with Ruby, there is a testing prototype of a Ruby scl. You can read all the instructions how to install and run the stack at [2] - but actually, this documentation is about an older version, which was actually named stack, so here are the up-to-date commands:

- add the repofile from http://bkabrda.fedorapeople.org/scl_1.8.7_01-27/scl_ruby_1.8.7.repo
- install the whole stack by "yum install scl_ruby_1.8.7" after adding the repo
- other commands from [2] apply, only substitute stack for scl (for example 'scl enable ruby_1.8.7 "irb"' will launch the ruby interactive console)

I think it would be great to consider this concept as an alternative (possibly sometime even replacement) to the current python/python3 state. What do you think, Pythonists? (And please don't kill me, I am just trying to suggest something, not break the current concept or start a flame war :) )

Regards,
Bohuslav "Slavek" Kabrda.

[1] http://koji.fedoraproject.org/koji/packageinfo?packageID=12980
[2] http://mmaslano.livejournal.com/6963.html