[Python-Dev] Python install layout and the PATH on win32 (original) (raw)

Carl Meyer carl at oddbird.net
Fri Mar 16 21:22:03 CET 2012

Hi Van,

On 03/16/2012 08:08 AM, Lindberg, Van wrote:

Changing the directory name is in fact a new and different (and much more invasive) special case, because distutils et al install scripts there, and that directory name is part of the distutils install scheme. Installers don't care where the Python binary is located, so moving it in with the other scripts has very little impact. So would changing the distutils install scheme in 3.3 - as defined and declared by distutils - lead to a change in your code? Alternatively stated, do you independently figure out that your virtualenv is on Windows and then put things in Scripts, etc, or do you use sysconfig? If sysconfig gave you different (consistent) values across platforms, how would that affect your code?

Both virtualenv and PEP 405 pyvenv figure out the platform at venv-creation time, and hard-code certain information about the correct layout for that platform (Scripts vs bin, as well as lib/pythonx.x vs Lib), so the internal layout of the venv matches the system layout on that platform. The key fact is that there is then no special-casing necessary when code runs within the virtualenv (particularly installer code); the same install scheme that would work in the system Python will also Just Work in the virtualenv.

I'm not concerned about changes to distutils/sysconfig install schems to make them more compatible across platforms from the POV of virtualenv; we can easily update the current platform-detection code to do the right thing depending on both platform and Python version.

I do share Éric's concern about whether distutils' legacy install schemes would be updated or not, and how this would affect backwards compatibility for older installer code, but that's pretty much orthogonal to virtualenv/pyvenv.

I don't want to make the internal layout of a virtualenv differ from the system Python layout on the same platform, which (IIUC) was Mark's proposal.

Hope that clarifies,

Carl

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