import subfolder in python

I have folder structure as follows:

/foo/trunk/mss/cloud

and

/foo/trunk/mss/model

my python file is located at subfolder model with name test.py I want to import all modules located in subfolder cloud so my code in test.py is:

import mss.cloud as cloud

but I got an error:

ImportError: No module named mss.clould

should I make any change on PYTHONPATH or anything else? any help is really appreciated.