The looming Python 3(000) monster

Toshio Kuratomi a.badger at
Fri Dec 5 18:32:15 UTC 2008

Michael DeHaan wrote:
> This isn't a huge problem to those who are only developing on the latest
> Fedora, per-se (other than getting over the initial hump), but it's
> pretty bad for someone who wants to keep a single codebase across EL 4
> (Python 2.3) and up, which I think a lot of us do.   That gets to be
> darn impossible and we have to double our involvement with code because
> we essentially have to maintain a differently-compatible fork for each
> project.
This is a problem that hasn't been brought up before.  We can keep
Fedora going on python-2.6, 2.7 (and 2.8 if it occurs) and gradually
move code close to py3.x-ish syntax by using the "from __future__ import
*" mechanism.  But that doesn't help with older distros running
python-2.5 or less.  I don't believe there's anyway around that, though.

As we move to python-2.6+ w/ 3.x features we'll have this problem no
matter when we actually move to python-3.  So we eventually (unless we
hold off on moving to python3 until python-2.6 is standard on all RHEL
releases) will be maintaining two trees of code no matter what.

If we maintain a python2 package and a python3 package in one version of
Fedora we'll have even more work.  Right now we can have an EL-5 and
Fedora-9&10 package that are compatible with 2.5.  A different version
can run on Fedora11 with the syntax ported to python-2.6's understanding
of what 3.x will be like.  If we have both python2-2.6 and python3-3.0
in Fedora11 we'll have to maintain separate py2 and py3 packages for
every python module we ship as well.  We should avoid this if we can.

Note that I think this decision is only partially within the powers of
the Fedora Project to decide.  If 80% of our upstream libraries move to
py3, we'll need to move to py3 sooner.  If 80% refuse to move off of
py2, we can take our time working on migration code.


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