setting PYTHONPATH to override system wide site-packages

Carl Banks pavlovevidence at gmail.com
Sun Mar 1 07:52:56 CET 2009


On Feb 28, 9:18 pm, per <perfr... at gmail.com> wrote:
> On Feb 28, 11:53 pm, per <perfr... at gmail.com> wrote:
>
>
>
> > On Feb 28, 11:24 pm, Carl Banks <pavlovevide... at gmail.com> wrote:
>
> > > On Feb 28, 7:30 pm, per <perfr... at gmail.com> wrote:
>
> > > > hi all,
>
> > > > i recently installed a new version of a package using python setup.py
> > > > install --prefix=/my/homedir on a system where i don't have root
> > > > access. the old package still resides in /usr/lib/python2.5/site-
> > > > packages/ and i cannot erase it.
>
> > > > i set my python path as follows in ~/.cshrc
>
> > > > setenv PYTHONPATH /path/to/newpackage
>
> > > > but whenever i go to python and import the module, the version in site-
> > > > packages is loaded. how can i override this setting and make it so
> > > > python loads the version of the package that's in my home dir?
>
> > > What happens when you run the command "print sys.path" from the Python
> > > prompt?  /path/to/newpackage should be the second item, and shoud be
> > > listed in front of the site-packages dir.
>
> > > What happens when you run "print os.eviron['PYTHONPATH']" at the
> > > Python interpreter?  It's possible that the sysadmin installed a
> > > script that removes PYTHONPATH environment variable before invoking
> > > Python.  What happens when you type "which python" at the csh prompt?
>
> > > What happens when you type "ls /path/to/newpackage" at your csh
> > > prompt?  Is the module you're trying to import there?
>
> > > You approach should work.  These are just suggestions on how to
> > > diagnose the problem; we can't really help you figure out what's wrong
> > > without more information.
>
> > > Carl Banks
>
> > hi,
>
> > i am setting it programmatically now, using:
>
> > import sys
> > sys.path = [....]
>
> > sys.path now looks exactly like what it looked like before, except the
> > second element is my directory. yet when i do
>
> > import mymodule
> > print mymodule.__version__
>
> > i still get the old version...
>
> > any other ideas?
>
> in case it helps, it gives me this warning when i try to import the
> module
>
> /usr/lib64/python2.5/site-packages/pytz/__init__.py:29: UserWarning:
> Module dateutil was already imported from /usr/lib64/python2.5/site-
> packages/dateutil/__init__.pyc, but /usr/lib/python2.5/site-packages
> is being added to sys.path
>   from pkg_resources import resource_stream

Ok then.  When pkg_resources is involved, who knows what behavior to
expect.

pkg_resources.py is a third-party module from PEAK (which
unfortunately a number of other third-party packages depend on, so it
can be hard to keep your installation free of it, but I digress).
Among other things no one knows about, it's a sort of run-time package
version management system.  It's possible, maybe, that some module
that runs on startup specifically requested and imported the version
of dateutils that's on the system path.  Which means, if you don't
properly appease pkg_resources, it could actually ignore your version
of the package even if it's earlier in the system path.  This is only
speculation, because who actually knows what's in the mind of
pkg_resources?, but if that is the reason, I won't be the one to tell
you how to fix it.

Here's something to try, however.  Set up your PYTHONPATH as you did
before, but also create an empty pkg_resources.py file in the
directory you specified.  Warning: this might make some packages
unusable.


Not-a-fan-of-pkg_resources-ly y'rs,

Carl Banks



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