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Subject: bug#27271: Avoiding =?UTF-8?Q?=E2=80=98propagated-inputs=E2=80=99?=
	for Python dependencies
Resent-Message-ID: <handler.27271.B27271.149710201515588@debbugs.gnu.org>
From: ludo@gnu.org (Ludovic =?UTF-8?Q?Court=C3=A8s?=)
References: <20170607092242.20565-1-ludo@gnu.org> <878tl2djh8.fsf@elephly.net>
	<871sqtpkfo.fsf@gnu.org> <87fuf8nbpv.fsf@fastmail.com>
Date: Sat, 10 Jun 2017 15:39:56 +0200
In-Reply-To: <87fuf8nbpv.fsf@fastmail.com> (Marius Bakke's message of "Fri, 09
	Jun 2017 22:32:44 +0200")
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To: Marius Bakke <mbakke@fastmail.com>
Cc: Ricardo Wurmus <rekado@elephly.net>, Hartmut Goebel <h.goebel@crazy-compilers.com>, 27271@debbugs.gnu.org

Heya,

(+Cc: Hartmut.)

Marius Bakke <mbakke@fastmail.com> skribis:

> Ludovic Court=C3=A8s <ludo@gnu.org> writes:

[...]

>> Perhaps we could modify =E2=80=98sys.path=E2=80=99 from the top of =E2=
=80=98__init__.py=E2=80=99 file to
>> get something similar to RUNPATH.  I=E2=80=99m not sure if there are any
>> downsides or gotchas.  Thoughts?
>
> Python actually has a native mechanism for setting up package-specific
> search paths: https://docs.python.org/3/library/site.html
>
> In short, it looks for a file "package.pth" where additional search
> paths can be specified (other sys.path manipulations are allowed too).

Looks good at first sight.

> I asked Hartmut about this during the python-build-system refactoring,
> and the counter-argument was that if package A and B depends on
> different versions of package C, odd failures could occur. I'm not
> convinced propagation sidesteps this problem, however:
>
> https://lists.gnu.org/archive/html/guix-devel/2016-10/msg00856.html

I think we=E2=80=99re in trouble anyway if multiple versions of a package e=
nd up
in the dependency graph because that=E2=80=99s not something Python supports
(the same is probably true for most languages, with the notable
exception of Node.)

Perhaps it would be worth making a PoC to see what happens with a small
set of packages?

(I=E2=80=99m not volunteering though, just trying to tweak others into doing
it.  :-))

Ludo=E2=80=99.