import numpy as np
import scipy

from scipy.interpolate import CubicSpline

x = np.array([0., 1., 2., 3.])
y = x ** 3
curve = CubicSpline(x, y, bc_type=((1, 0.), (1, 27.)), extrapolate=False)
assert abs(float(curve(1.5)) - 3.375) < 1e-10
assert abs(float(curve(1.5, 1)) - 6.75) < 1e-10
print(f"Midpoint value: {float(curve(1.5)):.6f}")