# Miller-Ranum listing 4.11 (inc. listing 4.4 too)

import math

def standardDev(alist):
    theMean = mean(alist)

    total = 0
    for item in alist:
        difference = item - theMean
        diffsq = difference ** 2
        total = total + diffsq

    sdev = math.sqrt(total/(len(alist)-1))
    return sdev

# listing 4.4:
def mean(alist):
    mean = sum(alist) / len(alist)
    return mean