def calcd(self, t):
    '\n        Calc first derivative\n        if t is outside of the input x, return None\n        '
    if (t < self.x[0]):
        return None
    elif (t > self.x[(- 1)]):
        return None
    i = self.__search_index(t)
    dx = (t - self.x[i])
    result = ((self.b[i] + ((2.0 * self.c[i]) * dx)) + ((3.0 * self.d[i]) * (dx ** 2.0)))
    return result
Calc first derivative
if t is outside of the input x, return None
def calcd(self, t):
    '\n        Calc first derivative\n        if t is outside of the input x, return None\n        '
    if (t < self.x[0]):
        return None
    elif (t > self.x[(- 1)]):
        return None
    i = self.__search_index(t)
    dx = (t - self.x[i])
    result = ((self.b[i] + ((2.0 * self.c[i]) * dx)) + ((3.0 * self.d[i]) * (dx ** 2.0)))
    return result