[Python-Dev] Remove site-packages?!? [was: [Distutils] PEP 376 - from pythonpkgmgr's point of view]

[Floris Bruynooghe]

On Wed, Jul 22, 2009 at 07:08:26PM -0400, Glenn Maynard wrote:
> On Wed, Jul 22, 2009 at 5:22 PM, M.-A. Lemburg<mal at egenix.com> wrote:
> > Maybe I've misunderstood some important detail, but how will
> > their "change" help with anything other than making their
> > distribution a non-standard Python installation ?
> 
> I think I'm a little confused, too, because Python supports the
> /usr|/usr/local separation just fine (setup.py install
> --prefix=/usr/local).
> 
> It seems like it's also using "dist-packages" instead of
> "site-packages".  That part, I don't understand at all--distribution
> packages should go in /usr/lib/pythonx.y/site-packages, and "site"
> packages go in /usr/local/pythonx.y/site-packages; /usr/local *itself*
> means "non-distribution site-installed stuff".  If that's what you're
> referring to, then at least on first impression I agree.

The way Debian does this isn't that stupid.  It solves the problem of
the sysadmin intalling Python distibutions for the system Python
without writing in the system locations, which is a very reasonable
thing to do.

Before Debian used dist-packages,
/usr/local/lib/pythonX.Y/site-packages was added to the sys.path of
the system Python and this was the location where a sysadmin should
add packages (although distutils did not default to that location, so
it wasn so it was still easy to mess up the system package
management).  But this caused trouble for people who installed their
own Python in /usr/local since now you have the same
/usr/local/lib/pythonX.Y/site-packages shared by 2 interpreters.

To solve this the system python moved to dist-packages instead, this
allows the local admin location to use
/usr/local/lib/pythonX.Y/dist-packages which does not conflict with
locally installed interpreters.  Together with this they changed
distutils to install to /usr/local/lib/pythonX.Y/dist-packages by
default, so that a sysadmin would have to go out of their way to mess
up the system package management.

This is a pretty neat solution to the problem.  But the weird thing
(IMHO) is that distutils-sig completely refuses to see this
requirement.  Generally it seems accepted that installing modules in
the system location (/usr/) is a bad thing, but last time it got
discussed there was a point blank refusal to accept that the local
admin needs a location in to install packages in.  I think it would be
great if Python instead provided a general guideline or best practice
for this situation which would be explained in the documentation.


Regards
Floris


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