If your Arduino is running with the latest Firmata firmware (aka sketch), you will notice that there are plenty of issues with binding implementations. This is because the Firmata protocol implements some new features of the past years and some bindings are not updated to work with Firmata > 2.0.
PIN = 12
DELAY = 2
PORT = '/dev/ttyACM0'
board = pyfirmata.Arduino(PORT)
Download it from here.