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