PiFace Digital IO no longer requires this module. I'm leaving it here in case anyone finds it useful. You can write to SPI directly from within Python 3.
Here is another version by someone else.
A Python SPI module
$ sudo python setup.py install$ python
>>> import spipy
>>> s = spipy.SPI(0, 0) # s refers to /dev/spidev0.0
>>> s.transfer((1, 2, 3)) # transfer three bytes
(0, 0, 0) # method returns three bytes (SPI is duplex)