## velocity
    def get_velocity(self):
        return ( (self.dx, self.dy) )
    def set_velocity (self, new_velocity):
        self.dx, self.dy = new_velocity
    velocity = property(get_velocity, set_velocity)

self.get_velocity() = lala
lala[1] = dx value and lala[2] = dy value

lala = self.get_velocity()

dx, dy = self.get_velocity()

d = self.get_velocity()
dx = d[0]
dy = d[1]