[Python-Dev] Python 3 as a Default in Linux Distros

[Brett Cannon]

On Wed, Jul 24, 2013 at 5:12 AM, Bohuslav Kabrda <bkabrda at redhat.com> wrote:

> Hi all,
> in recent days, there has been a discussion on fedora-devel (see thread
> [1]) about moving to Python 3 as a default.
> I'd really love to hear opinions on the matter from the upstream, mainly
> regarding these two points (that are not that clearly defined in my
> original proposal and have been formed during the discussion):
>
> - Should we point /usr/bin/python to Python 3 when we make the move?
> I know that pep 394 [2] deals with this and it says that /usr/bin/python
> may refer to Python 3 on some bleeding edge distributions - supposedly,
> this was added to the pep because of what Arch Linux did, not the other way
> round.
> As the pep says, the recommendation of pointing /usr/bin/python to Python
> 2 may be changed after the Python 3 ecosystem is sufficiently mature. I'm
> wondering if there are any more specific criteria - list of big projects
> migrated/ported or something like that - or will this be judged by what I'd
> call "overall spirit" in Python community (I hope you know what I mean by
> this)?
> In Fedora, we have two concerns that clash in this decision - being
> "First" (e.g. actively promote and use new technologies and also suggest
> them to our users) vs. not breaking user expectations. So we figured it'd
> be a good idea to ask upstream to get more opinions on this.
>
> - What should user get after using "yum install python"?
> There are basically few ways of coping with this:
> 1) Just keep doing what we do, eventually far in the future drop "python"
> package and never provide it again (= go on only with python3/python4/...
> while having "yum install python" do nothing).
> 2) Do what is in 1), but when "python" is dropped, use virtual provide (*)
> "python" for python3 package, so that "yum install python" installs python3.
> 3), 4) Rename python to python2 and {don't add, add} virtual provide
> "python" in the same way that is in 1), 2)
> 5) Rename python to python2 and python3 to python at one point. This makes
> sense to me from the traditional "one version in distro + possibly compat
> package shipping the old" approach in Linux, but some say that Python 2 and
> Python 3 are just different languages [3] and this should never be done.
> All of the approaches have their pros and cons, but generally it is all
> about what user should get when he tries to install python - either nothing
> or python2 for now and python3 in future - and how we as a distro cope with
> that on the technical side (and when we should actually do the switch).
> Just as a sidenote, IMO the package that gets installed as "python" (if
> any) should point to /usr/bin/python, which makes consider these two points
> very closely coupled.
>

A similar discussion broke out when Arch Linux switched python to point to
python3. This led to http://www.python.org/dev/peps/pep-0394/ which says
have python2/python3, and have python point at whatever makes the most
sense to you based on your users and version uptake (option 3/4). The key,
though, is adding python2 and getting your code to use that
binary  specifically so that shifting the default name is more of a
convenience than something which might break existing code not ready for
the switch.
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