[Numpy-discussion] Long term plans for dropping Python 2.7

[Ralf Gommers]

On Sat, Apr 15, 2017 at 5:19 PM, Nathaniel Smith <njs at pobox.com> wrote:

> On Fri, Apr 14, 2017 at 5:19 PM, Charles R Harris
> <charlesr.harris at gmail.com> wrote:
> > Hi All,
> >
> > It may be early to discuss dropping support for Python 2.7, but there is
> a
> > disturbance in the force that suggests that it might be worth looking
> > forward to the year 2020 when Python itself will drop support for 2.7.
> There
> > is also a website, http://www.python3statement.org, where several
> projects
> > in the scientific python stack have pledged to be Python 2.7 free by that
> > date.  Given that, a preliminary discussion of the subject might be
> > interesting, if only to gather information of where the community
> currently
> > stands.
>
> One reasonable position would that numpy releases that happen while
> 2.7 is supported upstream will also support 2.7, and releases after
> that won't.
>
> From numpy's perspective, I feel like the most important reason to
> continue supporting 2.7 is our ability to convince people to keep
> upgrading. (Not the only reason, but the most important.) What I mean
> is: if we dropped 2.7 support tomorrow then it wouldn't actually make
> numpy unavailable on python 2.7; it would just mean that lots of users
> stayed at 1.12 indefinitely. Which is awkward, but it wouldn't be the
> end of the world – numpy is mature software and 1.12 works pretty
> well. The big problem IMO would be if this then meant that lots of
> downstream projects felt that they had to continue supporting 1.12
> going forward, which makes it very difficult for us to effectively
> ship new features or even bug fixes – I mean, we can ship them, but
> no-one will use them. And if a downstream project finds a bug in numpy
> and can't upgrade numpy, then the tendency is to work around it
> instead of reporting it upstream. I think this is the main thing we
> want to avoid.
>

+1


>
> This kind of means that we're at the mercy of downstream projects,
> though – if scipy/pandas/etc. decide they want to support 2.7 until
> 2022, it might be in our best interest to do the same. But there's a
> collective action problem here: we want to keep supporting 2.7 so long
> as they do, but at the same time they may feel they need to keep
> supporting 2.7 as long as we do. And all of us would prefer to drop
> 2.7 support sooner rather than later, but we might all get stuck
>
because we're waiting for someone else to move first.
>

I don't quite agree about being stuck. These kind of upgrades should and
usually do go top of stack to bottom. Something like Jupyter which is
mostly an end user tool goes first (they announced 2020 quite a while ago),
domain specific packages go at a similar time, then scipy & co, and only
after that numpy. Cython will be even later I'm sure - it still supports
Python 2.6.


>
> So my suggestion would be that numpy make some official announcement
> that our plan is to drop support for python 2 immediately after
> cpython upstream does.


Not quite sure CPython schedule is relevant - important bug fixes haven't
been making it into 2.7 for a very long time now, so the only change is the
rare security patch.


> If worst comes to worst we can always decide to
> extend it at the time... but if we make the announcement now, then
> it's less likely that we'll need to :-).
>

I'd be in favor of putting out a schedule in coordination with
scipy/pandas/etc, but it probably should look more like
- 2020: what's on http://www.python3statement.org/ now
- 2021: scipy / pandas / scikit-learn / etc.
- 2022: numpy

Ralf


> Another interesting project to look at here is django, since they
> occupy a similar place in the ecosystem (e.g. last I checked numpy and
> django are the two most-imported python packages on github):
> https://www.djangoproject.com/weblog/2015/jun/25/roadmap/
> Their approach isn't directly applicable, because unlike us they have
> a strict time-based release schedule, defined support period for each
> release, and a distinction between regular and long-term support
> releases, where regular releases act sort of like
> pre-releases-on-steroids for the next LTS release. But basically what
> they settled on is philosophically similar to what I'm suggesting:
> they don't want an LTS to be supporting 2.7 beyond when cpython is
> supporting it. Then on top of that they don't want to support 2.7 in
> the regular releases leading up to that LTS either, so the net effect
> is that their last release with 2.7 support came out last week, and it
> will be supported until 2020 :-). And another useful precedent I think
> is that they announced this two years ago, back in 2015; if we make an
> announcement now, we'll be be giving a similar amount of warning.
>
> -n
>
> --
> Nathaniel J. Smith -- https://vorpus.org
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