Tobias,
I took a first look at your intrange.py and test_intrange.py files
from 2009-04-03:

* Which "errors" module are you refering to in main of intrange.py?
* The "warning" you are getting comes from the 
  test_invalidExpressions test.
  Found by running
    python test_intrange.py -v 
  So here is a run only showing the warning:
python test_intrange.py -v TestCase_intrange.test_invalidExpressions