Re: [gentoo-python] RFC: Redesign for 'best implementation' in python-r1

[Mike Gilbert]

On Sat, Dec 27, 2014 at 8:50 AM, Michał Górny <mgorny@g.o> wrote:
> Hello,
>
> The current design for getting the 'best implementation' is far from
> pretty. It pretty much relies on constant preference order, setting
> Python 2.7 over other implementations for practical reasons. As a side
> effect, various ebuilds rely on that particular order, e.g.:
>
>   DEPEND="doc? ( dev-python/epydoc[$(python_gen_usedep 'python2*')] )"
>   REQUIRED_USE="doc? ( $(python_gen_useflags 'python2*') )"
>
> which pretty much assumes that *if python2 is enabled*, then any
> version of it will be the best impl. I find this disgusting, and I'd
> like to replace it with something more explicit.
>

Yeah, relying python_compile_all running under python2.7 is no good.

>
> Specifically:
>
> 1. python_export_best becomes deprecated for good,
>
> 2. python_setup changes API to:
>
>   python_setup [<impl-wildcard>...]
>
> alike python_gen_* functions, defaulting to '*'. Now it chooses
> the best impl from implementations matching the specified patterns,
> e.g.:
>
>   python_setup 'python2*'
>
> would get the best version of CPython 2.
>
> 3. we introduce extra variable for distutils-r1 (oh cruel world, how
> should we name it?!) that applies wildcards to python_*_all() phases.
>

This sounds like a reasonable idea, and a natural extension of the
python_setup function.

>
> As for the choice within the list the algo needs to stay as-is for now.
> However, in the future we could either:
>
> a. respect EPYTHON and fallback to the other algo,
>
> b. respect pre-defined order i.e. 3.4 > 2.7,
>
> c. respect the order in PYTHON_COMPAT -- however that could be a little
> surprising to devs.
>
>
> What are your thoughts?

Starting/ending with EPYTHON from the environment seems wrong, and
doesn't seem to add value anyway.

I would prefer to stick with a predefined order unless someone can
present a case where the ebuild author really needs to control it.