[Python-Dev] Python 3 migration status update across some key subcommunities (was Re: 2.7 is here until 2020, please don't call it a waste.) (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Sun May 31 16:15:01 CEST 2015

On 31 May 2015 at 19:07, Ludovic Gasc <gmludo at gmail.com> wrote:

About Python 3 migration, I think that one of our best control stick is newcomers, and by extension, Python trainers/teachers. If newcomers learn first Python 3, when they will start to work professionally, they should help to rationalize the Python 3 migration inside existing dev teams, especially because they don't have an interest conflict based on the fact that they haven't written plenty of code with Python 2. 2020 is around the corner, 5 years shouldn't be enough to change the community mind, I don't know.

The education community started switching a while back - if you watch Carrie-Anne Philbin's PyCon UK 2014 keynote, one of her requests for the broader Python community was for everyone else to just catch up already in order to reduce student's confusion (she phrased it more politely than that, though). Educators need to tweak examples and exercises to account for a version switch, but that's substantially easier than migrating hundreds of thousands or even millions of lines of production code.

And yes, if you learn Python 3 first, subsequently encountering Python 2's quirks and cruft is likely to encourage folks that know both versions of the language to start advocating for a version upgrade :)

After accounting for the "Wow, the existing Python 2 install base is even larger than we realised" factour, the migration is actually in a pretty good place overall these days. The "enterprise" crowd really are likely to be the only ones that might need the full remaining 5 years of migration time (and they may potentially have even more time, if they're relying on a commercial redistributor).

Web frameworks have allowed Python 3 development for a while now, and with Django switching their tutorial to Python 3 by default, Django downloads via pip show one of the highest proportions of Python 3 adoption on PyPI. www.python.org itself is now a production Python 3 Django web service, and the next generation of pypi.python.org will be a Pyramid application that's also running on Python 3.

The dedicated async/await syntax in 3.5 represents a decent carrot to encourage migration for anyone currently using yield (or yield from) based coroutines, since the distinct syntax not only allows for easier local reasoning about whether something is an iterator or a coroutine, it also provides a much improved user experience for asynchronous iterators and context managers (including finally handling the "asynchronous database transaction as a context manager" case, which previous versions of Python couldn't really do at all).

The matrix multiplication operator is similarly a major improvement for the science and data analysis part of the Python community.

In terms of reducing barriers to adoption, after inviting them to speak at the 2014 language summit, we spent a fair bit of time with the Twisted and Mercurial folks over the past year or so working through "What's still missing from Python 3 for your use cases?", as Python 3.4 was still missing some features for binary data manipulation where we'd been a bit too ruthless in pruning back the binary side of things when deciding what counted as text-only features, and what was applicable to binary data as well. So 3.5 brings back binary interpolation, adds a hex() method to bytes, and adds binary data support directly to a couple of standard library modules (tempfile, difflib).

If I understand the situation correctly, the work Guido et al have been doing on PEP 484 and type hinting standardisation is also aimed at reducing barriers to Python 3 adoption, by making it possible to develop better migration tools that are more semantically aware than the existing syntax focused tools. The type hinting actually acts as a carrot as well, since it's a feature that mainly shows its value when attempting to scale a team to larger sizes (as it lets you delegate more of the code review process to an automated tool, letting the human reviewers spend more time focusing on higher level semantic concerns).

Finally, both Debian/Ubuntu and Fedora are well advanced in their efforts to replace Python 2 with Python 3 in their respective default images (but keeping Py2 available in their package repos). That work is close to finished now (myself, Slavek Kabrda, Barry Warsaw, and Matthias Klose had some good opportunities to discuss that at PyCon), although there are still some significant rough edges to figure out (such as coming up with a coherent cross-platform story for what we're going to do with the Python symlink), as well as a few more key projects to either migrate entirely, or at least finish porting to the source compatible subset of Python 2 & 3 (e.g. Samba).

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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