Re: 03/163: build/python: Add a new guix-pythonpath procedure.

[Ludovic Courtès]

Hi!

guix-commits@gnu.org skribis:

> apteryx pushed a commit to branch cu/farewell-to-pythonpath
> in repository guix.

Woow!

> commit c3c5bdd2b0ea4588ecba424fdbf6df101d967d3d
> Author: Maxim Cournoyer <maxim.cournoyer@gmail.com>
> AuthorDate: Fri Jan 22 09:34:33 2021 -0500
>
>     build/python: Add a new guix-pythonpath procedure.
>     
>     This procedure will be used in place where the static "PYTHONPATH" string 
> used
>     to be.
>     
>     * guix/build/python-build-system.scm (guix-pythonpath): New procedure.

[...]

> +(define (guix-pythonpath inputs)
> +  "Derive the GUIX_PYTHONPATH_X_Y string , with the major and minor version
> +numbers substituted for X and Y, respectively."
> +  (let ((python (assoc-ref inputs "python")))
> +    (string-append "GUIX_PYTHONPATH_"
> +                   (string-replace-substring (python-version python) "." 
> "_"))))

One pattern used elsewhere, notably for ‘GUIX_LOCPATH’, is to still keep
a single environment variable (that’d be ‘GUIX_PYTHONPATH’ here) but to
ensure that only MAJOR.MINOR sub-directories are taken into
consideration.

IOW, instead of having GUIX_PYTHONPATH_3_8 and GUIX_PYTHONPATH_2_7,
you’d have just GUIX_PYTHONPATH but Python 3.8 would only care about
3.8/ sub-directories while 2.7 would only care about 2.7/
sub-directories.

That’s perhaps easier to document and to deal with generally (you only
need to look at one specific environment variable).

Does that make sense?  I don’t know if it’s applicable in this case
though.

(I didn’t follow the PYTHONPATH discussion so apologies if this comment
is off!)

Anyhow, thanks for this long awaited change!

Ludo’.