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From: Scott Kitterman <debian@kitterman.com>
Newsgroups: linux.debian.maint.python
Subject: Re: PEP-517/PEP-518 Support In Debian
Date: Mon, 13 Apr 2020 14:10:01 +0200
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On Monday, April 13, 2020 5:18:53 AM EDT Dmitry Shachnev wrote:
> Hi Scott!
> 
> On Sun, Apr 12, 2020 at 06:31:57PM -0400, Scott Kitterman wrote:
> > This being roughly the mid-point in the development cycle, I thought it
> > might be good to see where we are in terms of future Python packaging
> > developments.
> > 
> > As I understand it, PEP-517 and PEP-518 are 'the future'.
> > 
> > I took a look at the presence of pyproject.toml files in the Debian
> > archive. There are currently 99 packages.  Of those, only 28 specify a
> > 'build-backend', which is required by 517/518 to be useful for building a
> > package.
> > 
> > 25 specify: build-backend = "setuptools.build_meta" (including setuptools)
> > 3 specify: build-backend = "flit_core.buildapi" (including flit)
> 
> pyqt5 and pyqt5webengine specify: build-backend = "sipbuild.api".

So they do.  They didn't show up in my codesearch.d.n results, that makes me 
wonder what else I missed.  If anyone has an idea of a better way to track 
this, please speak up.

> > If build-backend is not specified, the build system has to fall back to
> > setup.py.
> > 
> > I've recently package flit (just arrived in Testing) and written a flit
> > plugin for pybuild that's pending review for merging[1].  I also packaged
> > pep517 for our pip package, so that's available to support future Debian
> > tool development in this area.

P1otr merged the flit plugin a little while ago, so it'll be in the next dh-
python upload.

> > For the moment, I guess we are in reasonable shape, but it might be useful
> > to have a pybuild plugin to use PEP517/setuptools.build_meta in lieu of
> > setup.py with setuptools/distutils when available.  In the future, this
> > will be the primary API and the sooner we start to use it, the better.
> 
> One issue that comes to mind: how will we specify the install location in a
> way that will work with any backend? In other words, what is the replacement
> for distutils' --install-layout=deb?

I think the answer to that question is going to be build-backend specific.

The good news is that the legacy processing for setup.py with setuptools/
distutils will be around approximately forever, so a complete answer to the 
question isn't urgent.

One related question is if we are willing to bring pip into our package build 
process?  I took a quick look at python3-pep517 to see how hard it would be to 
add support for build-backend = "setuptools.build_meta"  to pybuild.  My quick 
look answer is not too hard if we are willing to bring pip into the process. 
If we aren't willing to involve pip (which does bring a lot of complexity), I 
think there will be substantially more Debian specific code required to support 
it.

I expect build-backend = "sipbuild.api" will need custom support as well, but 
I haven't looked into it at all.

Scott K
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