Recommend that you use the pyfrc simulator to test your code. Your problem will be immediately apparent when you actually run it.
To use the pyfrc simulator, get
pyfrc installed and just
run 'robot.py sim'.
When uploading the code to the robot, to see the output from your code (which would also show your problem), specify the --nc parameter to 'robot.py deploy' and it will launch a netconsole listener, which will show the output from your code.
You might benefit from the
RobotPy eclipse plugins that we just released, it makes running tests and such a lot easier.