When I'll probably be able to use Python assignment expressions

July 15, 2018

The big recent Python news is that assignment expressions have been accepted for Python 3.8. This was apparently so contentious and charged a process that in its wake Guido van Rossum has stepped down as Python's BDFL. I don't have any strong feelings on assignment expressions for reasons beyond the scope of this entry, but today I want to think about how soon I could possibly use them in my Python code, and then how soon I could safely use them (ie how soon they will be everywhere I care about). The answers to out to be surprising, at least to me (it's probably not to experienced Python hands).

The nominal Python 3.8 release schedule is set out in PEP 569. According to it, Python 3.8 is planned to be released in October of 2019; however, there's some signs that the Python people want to move faster on this (see this LWN article). If Python sticks to the original timing, Python 3.8 might make Ubuntu 20.04 LTS (released in April 2020 but frozen before then) and would probably make the next Fedora release if Fedora keeps to their current schedule and does a release in May of 2020. So at this point it looks like the earliest I'd be able to use assignment expressions is in about two years. If Python moves up the 3.8 release schedule significantly, it might make one Fedora release earlier (the fall 2019 release), making that about a year and a half before I could think about it.

There are many versions of 'can safely use' for me, but I'll pick the one for work. There 'safely use' means that they're supported by the oldest Ubuntu LTS release I need to run the Python code on. We're deploying long-lived Ubuntu 18.04 machines now that will only be updated starting in 2022, so if Python 3.8 makes Ubuntu 20.04 that will be when I can probably start thinking about it, because everything will be 2020 or later. That's actually a pretty short time to safe use as these things go, but that's a coincidence due to the release timing of Python 3.8 and Ubuntu LTS versions. If Python 3.8 misses Ubuntu 20.04 LTS, I'd have to wait another two years (to 2024) unless I only cared about running my code on Ubuntu 22.04.

Of course, I'm projecting things four to six years into the future and that's dangerous at the best of times. We've already seen that Python may change its release timing, and who knows about both Ubuntu and Fedora.

(It seems a reasonably safe guess that I'll still be using Fedora on my desktops over that time period, and pretty safe that we'll still be using Ubuntu LTS at work, but things could happen there too.)

The reason that all of this was surprising to me was that I assumed Python 3.8 was further along in its development if controversial and much argued over change proposals were getting accepted for it. I guess the arguments started well before Python 3.7 was released, which makes sense given the 3.7 release schedule; 3.7 was frozen at the end of January, so everyone could start arguing about 3.8 no later than then.

(The official PEP has an initial date of the end of February, but I've heard it was in development and being discussed before then, just not formalized yet as a PEP.)

PS: If Debian keeps to their usual release schedule, it looks like Python 3.8 on its original schedule would miss the next Debian stable version (Debian 10). It would probably miss it even on an aggressive release schedule that saw Python 3.8 come out only a year after 3.7, since 3.7 was released only a few weeks ago.

Written on 15 July 2018.
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Last modified: Sun Jul 15 23:35:50 2018
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