Re: switching to Python 3.x

[Han-Wen Nienhuys]

On Mon, Jan 6, 2020 at 8:21 PM David Kastrup <address@hidden> wrote:
> >> 1) Adapt the build system to find and require Python 3.
> >> patch:
> >> https://codereview.appspot.com/545370043
> >>
> >> 2) The largest part of the switch is running 2to3 which is now able to
> >> handle the rest of the conversion automatically. For reference, changes
> >> for current 'master' are here:
> >> https://codereview.appspot.com/573340043
> >>
> >> 3) Fix-up two places in the scripts afterwards:
> >> 3a) Remove the call to sys.setdefaultencoding which doesn't exist in
> >> Python 3.x (and is only available right now because of a dirty hack).
> >> 3b) Replace cgi.escape by html.escape. While not strictly needed, I
> >> think we should include this change because they removed cgi.escape in
> >> Python 3.8 after only deprecating it in Python 3.2. The replacement
> >> html.escape is only available since that Python 3.2, so we can't do
> >> this before switching.
> >> patch:
> >> https://codereview.appspot.com/561270043
> >>
> >>
> >> One point worth discussing is the future minimum version of Python 3.x.
> >> In the patch, I'm proposing Python 3.5 because it will allow us to
> >> address a few deprecation warnings, especially about module 'imp'.
> >> It should be available in most Linux distributions:
> >>  * CentOS 7 provides Python 3.6 since some minor releases
> >>  * Debian 9 (Stretch) has packages for Python 3.5, Debian 10 (Buster)
> >> even for Python 3.6
> >>  * Ubuntu 16.04 LTS has Python 3.5, version 18.04 LTS has Python 3.6
> >>
> >> Debian 8 (Jessie) only has Python 3.4, but even its LTS support will
> >> end next June (2020-06). Would it be acceptable to drop support for
> >> this distribution building 'master'?
> >> On the GUB side, I already added a spec for Python 3.7.4 (also for
> >> Windows via binary packages) and this worked successfully in September.
> >> Is there a major distribution missing that doesn't provide at least
> >> Python 3.5?
> >>
> >> Let me know what you think!
> >
> > So far, I've only received a single (positive) response off-list and a
> > bit of feedback on the posted patches. What do others think?
> > To make this explicit: The proposal is to drop support for Python 2
> > (now EOL), requiring everyone wishing to build LilyPond 'master' to
> > have an appropriate version of Python 3 available. This should be
> > sufficiently easy (see above), but I'd like to have consensus on this.
>
> When we switch over GUB, we also need to switch over the 2.20 branch.
> It's not just master that is affected.

But we only need to switch GUB to py3 when we package 2.21 with GUB.
We could kick this problem down the road until we really need a GUB
build of 2.21, which may well be a few months in the future, or never
if we decide to move to some other packaging mechanism (cf. the
discussion of Docker/Windows)

I don't think it's reasonable for us to ask Jonas to also package
python3 for GUB as a precondition to getting his patches in.

-- 
Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen