conflict between multiple installs of python (linux)

[david]

You learn something new every day:

On my ubuntu, update-manager is supposed to use the python2.5
installed on /usr/bin. Well, I had subsequently installed a whole
bunch of stuff in /usr/local (/usr/local/bin/python and /usr/local/lib/
python2.5 etc), which I have happily been using for development for a
year. I had thought that the two pythons were completely independent.

Well, I was wrong. When /usr/bin/python2.5 runs, *by default*, it
adds /usr/local/lib/python2.5 to its sys path - and apparently there
are things in /usr/local which are inconsistent with those at /usr
(not suprising).

I have fixed the problem - but I had to modify the actual update-
manager .py file itself. At the beginning, I set the sys.path in
python *explicitly* to not include the /usr/local stuff.

But this is clearly a kludge. My question: how do I keep the Ubuntu
python stuff at /usr/bin/python2.5 from adding /usr/local/lib/
python2.5 to the import search path in a clean and global way? I
really want both pythons completely isolated from one another!

Thankyou.