
On Fri, Apr 14, 2017 at 5:19 PM, Charles R Harris <charlesr.harris@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.
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. 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. 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 :-). 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