Python is installed in a local directory.
My directory tree looks like this:
(local directory)/site-packages/toolkit/interface.py
eg: /etc/environment
PYTHONPATH=$PYTHONPATH:/opt/folder1:/opt/folder2
/opt/folder1/foo
/opt/folder2/foo
And, if you are trying to import foo file, python will not know which one you want.
from foo import ... >>> importerror: no module named foo