The PiFace Digital Input/Output module (PyPI).
http://pifacedigitalio.readthedocs.org/
You can also find the documentation and some examples installed at:
/usr/share/doc/python3-pifacedigitalio/
Make sure you are using the lastest version of Raspbian:
$ sudo apt-get update
$ sudo apt-get upgrade
Install pifacedigitalio (for Python 3 and 2) with the following command:
$ sudo apt-get install python{,3}-pifacedigitalio
Test by running the blink.py program:
$ python3 /usr/share/doc/python3-pifacedigitalio/examples/blink.py