poliom lagr

from matplotlib import pyplot as plt
X=[-3, -2, -1, 0, 1, 2, 3]
Y=[9, 4, 1, 0, 1, 0, 0]

cur_x = 4
def lagr(x, y, cur_x):
    res = 0.0
    n = len(X)
    for i in range(n):
        l_i=1.0
        for j in range(n):
            if i == j:
                continue
            l_i*=(cur_x-float(x[j]))/(x[i]-x[j])
        res+=y[i]*l_i
    return res

X_new = []
Y_new = []
step=0.001
X_start,X_stop = X[0],X[-1]
while X_start<X_stop+step:
    X_new.append(X_start)
    Y_new.append(lagr(X, Y, X_start))
    X_start+=step
plt.plot(X, Y)
plt.plot(X_new,Y_new)
plt.show()