Importing modules from parent folder

I am running Python 2.5.

This is my folder tree:

ptdraft/
  nib.py
  simulations/
    life/
      life.py

(I also have __init__.py in each folder, omitted here for readability)

How do I import the nib module from inside the life module? I am hoping it is possible to do without tinkering with sys.path.

Note: The main module being run is in the ptdraft folder.

from Importing modules from parent folder