package import question

[Phoe6]

Hi all,
I have the following directory structure:

wallpaper/
              -main.py
              -ng/
                 -- __init__.py
                 -- setdesktop.py
              -yb/
                 -- __init__.py
                 -- setdesktop.py

>From main.py, I would like to do:
import ng
import yb
ng.setdesktop.run()
yb.setdesktop.run()

But it is not working! when I import the package, the modules present
inside the package are getting imported.

However, following the python document if I do
import ng.setdesktop
import yb.setdesktop

ng.setdesktop.run()
yb.setdesktop.run()
Works fine.

I would like to use the notation.
import <my_package_name>
and use the modules inside the package in the dotted module notation.
What should I do the enable such a kind of imports.

Please let me know.

Thank you.
Senthil