Re: [PATCH 3/7] configure: Look for auxiliary Python installations

[John Snow]

On Fri, Feb 10, 2023 at 2:45 PM Eric Blake <eblake@redhat.com> wrote:
>
> On Thu, Feb 09, 2023 at 10:40:30AM -0500, John Snow wrote:
> > At the moment, we look for just "python3" and "python", which is good
> > enough almost all of the time. But ... if you are on a platform that
> > uses an older Python by default and only offers a newer Python as an
> > option, you'll have to specify --python=/usr/bin/foo every time.
> >
> > We can be kind and instead make a cursory attempt to locate a suitable
> > Python binary ourselves, looking for the remaining well-known binaries.
> >
> > This configure loop will prefer, in order:
> >
> > 1. Whatever is specified in $PYTHON
> > 2. python3
> > 3. python
> > 4. python3.11 down through python3.6
>
> Makes sense.
>
>
> >  python=
> > +first_python=
> >  explicit_python=no
> > -for binary in "${PYTHON-python3}" python
> > +# A bare 'python' is traditionally python 2.x, but some distros
> > +# have it as python 3.x, so check in both places.
> > +for binary in "${PYTHON-python3}" python python3.{11..6}
>
> This does not match your commit message. If $PYTHON is set but fails,
> you never check python3.  Pre-existing, but now that you're calling it
> out as intended, it may be better to write the list prefix as:
>
> for binary in $PYTHON python3 python ...
>
> except that it mishandles $PYTHON containing space, so you want the
> quotes, but you don't want to test an empty binary or waste time
> testing python3 twice, so more precise could be:
>
> for binary in "${PYTHON-python3}" ${PYTHON:+python3} python ...

Yep. I wonder if it's worth helping people work around broken
environment variables at all, but, eh, you already solved the more
difficult case, so I can include it.

(Well, pending other discussions, I s'pose.)

>
> Meanwhioe, your use of {11.6} is a bashism, but configure is /bin/sh.
> It would be nice if you could use $(seq -f python3.%g 11 -1 6), but
> that's probably too specific to GNU Coreutils and won't work on other
> platforms; and open-coding it in a shell loop isn't going to be any
> prettier.  So you'll be safest if you just manually spell it out:
>
> python3.11 python3.10 ...

Oh, icky.  Well, OK. Thanks for pointing it out before it became a
problem somewhere.

>
> --
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
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>