import math
#
#   An object of class StatCalc can be used to compute several simple statistics
#   for a set of numbers.  Numbers are entered into the dataset using
#   the enter(double) method.  Methods are provided to return the following
#   statistics for the set of numbers that have been entered: The number
#   of items, the sum of the items, the average, and the standard deviation.
#

class StatCalc(object):

    def __init__(self):
        self.count = 0
        self.sum   = 0.
        self.squareSum   = 0.

    def enter(self, num):
        " Add the number to the dataset."
        self.count += 1
        self.sum += num
        self.squareSum += num*num
   

    def getCount(self): 
        " Return number of items that have been entered."
        return self.count
   
    def getSum(self): 
        " Return the sum of all the items that have been entered."
        return self.sum
   
    def getMean(self): 
        " Return average of all the items that have been entered."
        return self.sum / self.count
   
    def getStandardDeviation(self): 
        " Return standard deviation of all the items that have been entered."
        return math.sqrt( self.squareSum/self.count - self.getMean()**2 )
   
# end of class StatCalc