From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Hinsen <konrad.hinsen@fastmail.net>
Subject: Re: Down with PYTHONPATH!
Date: Mon, 17 Jun 2019 12:20:12 +0200
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org, Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>

Hi Ludo,

> How does virtualenv work, if not by setting PYTHONPATH?

It creates a new filetree corresponding to a complete new Python
installation, and the uses soft links to share most of the actual files
with the parent installation.

> Setting up an environment all about augmenting the search path, so I
> naively thought that virtualenv sets PYTHONPATH or the corresponding
> Python variable.

PYTHONPATH only adds directories to the search path. The standard
library and packages installed via pip are already on the search path
before PYTHONPATH is looked at. So virtualenv could not work by
modifying PYTHONPATH.

Konrad.