On Thu, Jun 21, 2012 at 12:57 AM, Nick Coghlan <ncogh...@gmail.com> wrote:
>
> Standard assumptions about the behaviour of site and distutils cease to be 
> valid once setuptools is installed
…
> - advocacy for the "egg" format and the associated sys.path changes that 
> result for all Python programs running on a system
…
> System administrators (and developers that think like system administrators 
> when it comes to configuration management) *hate* what setuptools (and 
> setuptools based installers) can do to their systems.

I have extensive experience with this, including quite a few bug
reports and a few patches in setuptools and distribute, plus
maintaining my own fork of setuptools to build and deploy my own
projects, plus interviewing quite a few Python developers about why
they hated setuptools, plus supporting one of them who hates
setuptools even though he and I use it in a build system
(https://tahoe-lafs.org).

I believe that 80% to 90% of the hatred alluded to above is due to a
single issue: the fact that setuptools causes your Python interpreter
to disrespect the PYTHONPATH, in violation of the documentation in
http://docs.python.org/release/2.7.2/install/index.html#inst-search-path
, which says:

"""
The PYTHONPATH variable can be set to a list of paths that will be
added to the beginning of sys.path. For example, if PYTHONPATH is set
to /www/python:/opt/py, the search path will begin with
['/www/python', '/opt/py']. (Note that directories must exist in order
to be added to sys.path; the site module removes paths that don’t
exist.)
"""

Fortunately, this issue is fixable! I opened a bug report and I and a
others have provided patches that makes setuptools stop doing this
behavior. This makes the above documentation true again. The negative
impact on features or backwards-compatibility doesn't seem to be
great.

http://bugs.python.org/setuptools/issue53

Philip J. Eby provisionally approved of one of the patches, except for
some specific requirement that I didn't really understand how to fix
and that now I don't exactly remember:

http://mail.python.org/pipermail/distutils-sig/2009-January/010880.html

Regards,

Zooko
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