Re: gnulib-tool: Use the Python implementation by default

[Pádraig Brady]

On 27/04/2024 14:32, Bruno Haible wrote:
> Hi Pádraig,
>
> > > +    if (python3 --version) >/dev/null 2>/dev/null \
> > > +       && case `python3 --version 2>&1` in
> > > +            Python\ 3.[0-6] | Python\ 3.[0-6].*) false ;;
> > > +            Python\ 3.*) true ;;
> > > +            *) false ;;
> > > +          esac; then
> >
> > It may be preferable to state the supported version directly,
>
> I wanted a short warning message. In most cases the absence of python3
> will be the problem. It should be rare than anyone still uses an old
> version.
>
> > and replace the above 6 lines with:
> >
> >     if python3 -c 'import sys; sys.exit(not sys.version_info >= (3,7))' 
> > 2>/dev/null; then
>
> Thanks for the hint. I admit that I did not think at it. But is it
> actually better?

Only that's it's shorter, and more directly states the supported version.
No biggie, just a suggestion.


> Are there alternative Python implementations, which could be installed under
> the name 'python3'?

So this is a general question, unrelated to my particular suggestion.
I think the version check is fine, and should be quite independent from python 
implementation.
Possible drop in replacements for the python3 command might be ...

... pypy, which separates its implementation version from python language 
support version:
$ dnf install pypy3
$ pypy3

>>>> sys.pypy_version_info
sys.pypy_version_info(major=7, minor=3, micro=15, releaselevel='final', 
serial=0)
>>>> sys.version_info
sys.version_info(major=3, minor=10, micro=13, releaselevel='final', serial=0)

... cinder, which is very close to cpython ...
$ dnf install docker
$ sudo systemctl start docker
$ sudo setfacl --modify user:$USER:rw /var/run/docker.sock
$ docker run -it --rm ghcr.io/facebookincubator/cinder-runtime:cinder-3.10

Python 3.10.5+cinder (main, Apr 26 2024, 22:00:58) [GCC 10.3.1 20210422 (Red 
Hat 10.3.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.version_info
sys.version_info(major=3, minor=10, micro=5, releaselevel='final', serial=0)


There are no other real contenders for drop in python 3 replacement.
For example codon or mojo are not designed as drop in replacements.
I expect any future drop in replacements would follow the model above.

> Note also that your snippet would not replace the 6 lines of code, only the
> last 5 lines, because with Solaris 10 /bin/sh your snippet produces the
> diagnostic
>    python3: not found

Out of interest, I dug out an old dsa ssh key from a backup, to get access to a 
solaris 10 machine.
Testing shows that a subshell does avoid that issue, so the following works:

  if (python3 -c 'import sys; sys.exit(not sys.version_info >= (3,7))') 
2>/dev/null; then

cheers,
Pádraig