from sympy import * 
x, y, z, t = symbols('x y z t') 

def coefficient(XX, i):
	n = len(XX)
	L = 1
	for j in range(0,n ):
		if i != j:
			L = L * (x - XX[j])
			L = L / (XX[i] - XX[j])
	return L

print(coefficient([1, -3, 8], 0))
print(expand(coefficient([1, -3, 8], 0)))
print(factor(coefficient([1, -3, 8], 0)))