polinom langranga s new znachenia

from matplotlib import pyplot as plt
X=[-1.5,-0.75,0,0.75,1.5]
Y=[-14.1014,-0.931596,0,0.931596,14.1014]

cur_X= 2
def L(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=0.1
X_start,X_stop=X[0], X[-1]
while (X_start<X_stop+step):
    X_new.append(X_start)
    Y_new.append(L(X,Y,X_start))
    X_start+=step
plt.plot(X_new,Y_new)
plt.show()
print L()