To help me track problems in Python code (yes, even sometimes in my own...) I usually rely on good-old print/trace debugging. Owing to Python's speed of interpretation and execution, this is a pretty convenient approach. Python does have its own interactive debugger though - pdb - for those odd occasions when it's desirable to poke about in a program while it's running. The debugging mode in Emacs even supports pdb by default, but there's a little snag: you probably don't have a pdb in your path, so M-x pdb will just fail. Solution? Add a pdb script to your path and make it executable

#!/bin/sh
pdb_path=`python -c "import pdb, sys; sys.stdout.write(pdb.__file__ + '\n')"`
exec python ${pdb_path} "$@"