Definite Integration

def simpson(f, a, b, n):
    h = float(b-a)/n
    x = lambda i: (a + i*h)
    s1 = 0
    for j in xrange(1,(n/2)):
        s1 += f(x(2*j))
    s1 *= 2
    s2 = 0
    for j in xrange(1,(n/2)+1):
        s2 += f(x(2*j - 1))
    s2 *= 4
    s = h/3*(f(x(0)) + f(x(n)) + s1 + s2)
    return s

def (f, a, b, n):
    s = 0
    for k in xrange(1, n):
        s += f(a + ((k*(b-a))/n))
    s += 0.5*(f(a) + f(b))
    s *= (b-a)/n
    return s