def __init__(self, x, y):
    self.s = self.__calc_s(x, y)
    self.sx = Spline(self.s, x)
    self.sy = Spline(self.s, y)
def __init__(self, x, y):
    self.s = self.__calc_s(x, y)
    self.sx = Spline(self.s, x)
    self.sy = Spline(self.s, y)