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

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi Harmut!

Hartmut Goebel <h.goebel@crazy-compilers.com> writes:

> Hi schrieb Maxim,
>> Sorry for the delay.
>
> No problem, I reward this with another delay ;-) (Just kidding ;-)
>
>
>> Hartmut Goebel <h.goebel@crazy-compilers.com> writes:
>>
>>> 2) This does not remove duplicates and does not honor .pth files in
>>> the respective directories - which might still be used. Thus
>>> site.addsitedir() should be called for adding the paths. This also
>>> takes care about duplicates.
>> I confess I didn't pay attention to .pth files, which mostly seemed like
>> legacy cruft to me; are they still used in the context of PEP 517 and
>> modern Python packaging?
>
> I can't tell for sure. (I rinember to have seen a note about .pth still
> being used in some setuptool-tick, but can't find it now.) Anyhow, since
> site.py still supports it, I would prefer to be on the save side and
> support it, to.
>
>> The problem with calling site.addsitedir is
>> that it simply appends to sys.path.  We want to splice in the content of
>> GUIX_PYTHONPATH at a controlled location.
>
> site.addsitedir takes an option second arguments where the paths are
> collected into.
>
>
>>> 4) Since PYTHONPATH is evaluated prior to importing sitecustomize, any
>>> sitecustominze.py in the user's path will overwrite our file, thus
>>> inhibiting our paths to be added. Not sure this is what we want in Guix.
>> I asked guidance on the #python channel on freenode and was recommended
>> to use sitecustomize.py for this purpose; reading the doc here seems to
>> confirm our usage of it is as intended [0]:
>
> IC.
>
>
>>> 6) Please add some more comments to the code explaining the idea.
>> I was under the impression the code was concise enough to forego with
>> verbose explanations; I'd rather keep it this way.
>
> Please add some comments. I had a hard time understanding it - and I was
> not even sure I understood, see my question (1).

I'm spread thin right now, so if you could prepare a patch addressing
the above for me to review, that'd be much appreciated.  Otherwise I'll
get to it, but it won't be before some time.

> Another point, which came into my mind just now: Do virtuall
> environments still work as expected? (With --system-site-packages,
> packages in the profile are available, but venv-packages overwrite.
> Without ----system-site-packages packages in the profile are *not*
> available.)

Yes!  This was the main motivation behind this change.

Thank you,

Maxim