accelerate.py

class Accelerate( IntervalAction ):
    def init(self, other, rate = 2):
        self.other = other
        self.rate = rate
        self.duration = other.duration

    def start(self):
        self.other.target = self.target
        self.other.start()

    def update(self, t):
        self.other.update( t**self.rate )

    def __reversed__(self):
        return Accelerate(Reverse(self.other), 1.0/self.rate)