[Qgis-user] Changes in Python versions on QGIS 3.18

[Greg Troxel]

Nyall Dawson <nyall.dawson at gmail.com> writes:

> On Thu, 25 Mar 2021 at 10:41, Pedro Camargo <veigacamargo at gmail.com> wrote:
>>
>> Hello,
>>
>> I am not sure this is the appropriate mailing list to send this, but here it goes.
>>
>> I have noticed that QGIS 3.18 for Windows has shipped with Python 3.9, after having updated to 3.8 just a couple of versions ago.
>
> I'm curious -- what's the pain in a Python update? They usually have
> very little harmful impact on python code.

Speaking as someone who works on a portable packaging system (pkgsrc),
not particularly related to qgis:

We tend to add new python versions more or less immediately (in
parallel), change the default with due consideration, and then retire
older versions when they are both out of support and no longer needed
(in that anything that works with the old version also works with some
newer version).

It's quite common for python packages to fail with new 3.x versions, so
we are somewhat shy about bumping the default version.

We just a few months ago switched from 3.7 to 3.8, and that was probably
overdue.  At the time, some asked "why not 3.9" and the answer on
looking was pretty clear: a fairly large number of packages did not
build/work with 3.9.  I am not sure it was 10%, but it was enough that
having those packages be missing/broken with the default version seemed
like a bigger minus than the positive benefit of a 3.8->3.9 move.

So yes, for a given minor bump and a given package, the odds of trouble
are fairly low, but the odds that a group of 100 packages has zero
trouble is also pretty low, in my experience.

Depending on packaging norms, the timeline involves not only the change
necessary for 3.N++ to be accomodated, but then a release made.  I
expect pkgsrc will ask the "is it time for 3.9?" question again in
April/May (we have quarterly cycle), and it feels like even odds if it
will be time.

So I am a bit surprised about the official windows installer moving to
3.9 already.  (But I don't use Windows, and I build qgis from sources
via pkgsrc, currently python 3.8.)
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