Switching to Python 3

[David Malcolm]

On Mon, 2012-08-13 at 03:09 -0400, Bohuslav Kabrda wrote:
> ----- Original Message -----
> > On 08/06/2012 04:22 AM, Toshio Kuratomi wrote:
> > > The only distribution that has switched is arch.  When they did
> > > there was
> > > a big uproar about how arch was doing something wrong which
> > > eventually
> > > resulted in that PEP.
> > 
> > Yeah, we mainly wrote PEP 394 in order to nudge *everyone else* into
> > providing a /usr/bin/python2 symlink to help deal with Arch making
> > their
> > bold leap into the unknown (as well as going on record that we think
> > switching it *right now* is still a bad idea). There's "bleeding
> > edge"
> > and then there's "tap dancing on razor blades in your bare feet" :P
> > 
> > To be honest, I expect that the long term outcome will be that
> > "/usr/bin/python" becomes solely the preserve of the OS, with all
> > cross-platform scripts and applications using "/usr/bin/pythonX",
> > software collections, or language level virtual environments.
> > 
> > From an end user perspective, having things mostly compatible with
> > both
> > 2 and 3 should come *before* that symlink gets flipped rather than
> > after.
> > 
> > Cheers,
> > Nick.
> > 
> 
> Ok, then I would suggest using Tom Spura's idea about making only
> python2- and python3- packages (maybe with the virtual python-
> provides for python2- packages, as Toshio has mentioned). We could
> target this for F19 and we could also start helping various upstreams
> with switching to python 3 and see where this will take us. Does that
> sound good?
If we're looking at this kind of change (python2-foo and python3-foo),
how about some other prefixes:
  * python2-debug-foo (or somesuch) for a build of the package against
the --with-pydebug python2 package
  * python3-debug-foo
  * pypy-foo for the package built against PyPy

FWIW an old idea I had for revamping how we maintain Python packages can
be seen here:
http://lists.fedoraproject.org/pipermail/python-devel/2010-March/000213.html
with some further ideas here:
https://fedoraproject.org/wiki/DaveMalcolm/PythonIdeas
(you can tell that page is old, it still mentions Unladen Swallow and
Pynie...)

I still like the basic idea: introduce a tool that captures the info on
python runtimes for a given release in one place, and use it
programmatically within specfiles to avoid copy&paste.  Although the
proposal isn't complete (how to handle exclusions?), I'm still fond of
it.

Another idea would be to use the Software Collections tool seen here:
  https://fedorahosted.org/SoftwareCollections/
I known that people within Red Hat have been looking at using that in
the RHEL context, and some of that is likely to be appropriate for EPEL
too - though AIUI it's a shift in model from one build per src.rpm to
multiple builds per src.rpm

Hope this is helpful
Dave