Online average counter

gistfile1.py

import math

class Calculator(object):
    def __init__(self):
        self.__count = 0
        self.__sum = 0.0
        self.__sqsum = 0.0

    @property
    def average(self):
        return self.__sum / float(self.__count)

    @property
    def distribution(self):
        return math.sqrt(self.__count * self.__sqsum - self.__sum ** 2) / self.__count

    def add_number(self, num):
        self.__count += 1
        self.__sum += num
        self.__sqsum += num ** 2

    def add_iter(self, iter):
        for num in iter:
            self.add_number(num)

if __name__ == '__main__':
    c = Calculator()
    for i in range(-2, 3):
        c.add_number(i)
        print i, c.average, c.distribution