def stats(lista):
    """ returns mean and variance of the list lista.
        assumes that lista is not empty """
    mean = sum(lista)/len(lista)
    variance = 0
    for element in lista:
        variance += (element-mean)**2
    return mean, variance/len(lista)

lista = [1,1,1,2,2,2,2,2,3,3]
mu, sigma2 = stats(lista)

def length(vector):
    """ calculates the length of the vector, assumed to
        be a three-tuple of floating point numbers or
        integers"""
    x, y, z = vector
    return (x*x+y*y+z*z)**0.5