Python math and stats functions

stats.py

# $Date: 2010-10-29 16:09:50 -0400 (Fri, 29 Oct 2010) $
# Filename: stats.py
#
# A bunch of math/stats functions
import math

'''calculate average'''
def calcAvg(ls):
    n, mean = len(ls), 0.0

    if n <= 1:
        return ls[0]

    # calculate average
    for el in ls:
        mean = mean + float(el)
    mean = mean / float(n)

    return mean
 
'''calculate standard deviation'''
def calcSD(ls):
    n = len(ls)

    if n <= 1:
        return 0.0

    mean, sd = calcAvg(ls), 0.0

    # calculate stan. dev.
    for el in ls:
        sd += (float(el) - mean)**2
    sd = math.sqrt(sd / float(n-1))

    return sd

'''calculate both average and standard deviation'''
def calcAvgAndSD(ls):
    return calcAvg(ls), calcSD(ls)

'''calculate the median'''
def median(ls):
    ls = sorted(ls)
    n = len(ls)
    median = 0

    if n % 2 == 0:
        median = (ls[(n/2)-1] + ls[n/2])/2.0
    else:
        median = ls[((n+1)/2)-1]

    return median

'''calculate the lower quartile - defined as median of the lower
half of the data. if ls has odd number of elements, the median is
not included in the calculation'''
def lowerQuartile(ls):
    ls = sorted(ls)
    n = len(ls)
    return median(ls[0:(n/2)])

'''same as lowerQuartile() but calculating the upper quartile'''
def upperQuartile(ls):
    ls = sorted(ls)
    n = len(ls)
    return median(ls[((n+1)/2):])

'''Determine whether a number is between two numbers x and y. Return True if
yes, False otherwise.'''
def isBetween(i, x, y):
    return (i >= x and i <= y)

if __name__ == "__main__":
    print isBetween(4.1,1,5)

    ls = [4, 5, 6]
    print calcAvg(ls)
    print calcSD(ls)
    print calcAvgAndSD(ls)