utils.py

class Timer(object):
    """ A Timer that can periodically call a given callback 
        function.
        
        After creation, you should call update() with the 
        amount of time passed since the last call to update() 
        in milliseconds.
        
        The callback calls will result synchronously during these
        calls to update()
    """
    def __init__(self, interval, callback, oneshot=False):
        """ Create a new Timer.
        
            interval: The timer interval in milliseconds
            callback: Callable, to call when each interval expires
            oneshot: True for a timer that only acts once
        """
        self.interval = interval
        self.callback = callback
        self.oneshot = oneshot
        self.time = 0
        self.alive = True
        
    def update(self, time_passed):
        if not self.alive:
            return
            
        self.time += time_passed
        if self.time > self.interval:
            self.time -= self.interval
            self.callback()
            
            if self.oneshot:
                self.alive = False