
It's all there, just overload the "button_down" method of Window (no question mark), just like in the tutorial game :)
button_down is the callback that you use for one-time events, button_down? is the check that you use in your logic for holding keys down. You can also combine both, i.e. shoot on the first button_down and then count the ticks from then on, repeating the fire after every 10, etc.