polin

from matplotlib import pyplot as plt
def pr(x,y,cur):
    res=0.0
    for i in range (len(x)):
        li=1.0
        for j in range (len(x)):
            if (i!=j):
                li*=(cur-float(x[j]))/(x[i]-x[j])
        res+=y[i]*li
    return res
x=[1,2,3,4,5,6]
y=[1,8,27,64,125,216]
x_new=[]
y_new=[]
step=0.0005
x_start,x_stop=x[0],x[-1]
while x_start<x_stop+step:
    x_new.append(x_start)
    y_new.append(pr(x,y,x_start))
    x_start+=step
plt.plot(x_new,y_new)
plt.plot(x,y)
plt.show()
print pr (x,y,1)