I would like to share a story about how I killed a couple of hours recently. I write on rospy a small architecture to work with a robot. Since there are no good examples and I’m not an expert in the python, without thinking twice, I added the path to the project (let it be ~/work/src/coolp) in PYTHONPATH. Then I added empty __init__.py directly to the root of proper packages ( eg. coolp/control/__ init__.py next to the scripts that you want to import coolp/control/control_arm.py) and now at any place where I need this script – from control.control_arm import LeftArm.