from sympy import *
def moyenne(t) :
    return sum(t)/len(t)
def variance(t) :
    n = len(t)
    moy = moyenne(t)
    total = 0
    for k in range(n) :
        total = total + (t[k]-moy)**2
    return total/n
def ecartType(t) :
    return sqrt(variance(t))