Setting up nxt-python in OS X requires a little extra effort. As described on its installation page, you will need to install LightBlue, which is Bluetooth API for Python. And in order to install LightBlue to OS X 10.6, a few manual operation needs to be done.

Nevertheless, the installation of LightBlue failed. It turns out I need to add the directory of PyObjC to my PYTHONPATH in order for it to work, which in my case (Python 2.6) is:

/System/Library/Frameworks/Python.framework/Versions/2.6/Extras/lib/python/PyObjC

Also, wherever you have placed the LightAquaBlue directory (the one in Step 2 for Mac OS 10.6 users, not the one in Step 3) will need to be in PYTHONPATH, too, e.g.:

/Library/Python/2.6/site-packages

Then you should be able to setup and install nxt-python without a problem.