Importing python packages into node files

edit

I have set up my ROS package with the following layout:

packagename
  CMakeLists.txt
  package.xml
  |- src/
    |- packagename/
      |- __init__.py
      |- package_file.py
  |- scripts/
    |- node_file.py

And in node_file.py, I'd like to be able to do

from packagename import package_file

But I get cannot import name package file.

Am I laying this out correctly? How do I make my python package visible to node_file.py? I am using ROS Hydro in Ubuntu 12.04 LTS.