general sorting algorithms in python

sorting.py

#!/usr/bin/env python

from math import sqrt
import random

def bubble_sort(a):
    """
    basic sorting method -- bubble sort
    """
    s = len(a)
    for i in range(0, s):
        for j in range(i, s):
            if a[i]>a[j]:
                a[i], a[j] = a[j], a[i]
    return a

def selection_sort(a):
    """
    select sort - time complexity: O(n^2),
    out performs 'bubble sort'
    """
    s = len(a)
    for i in range(0, s):
        m = i
        for j in range(i+1, s):
            if a[j]<a[m]:
                m = j
        a[i], a[m] = a[m], a[i]
    return a

def insertion_sort(a):
    """
    insert sort -- time complexity: O(n^2), 
    generally out performs 'select sort'
    """
    s = len(a)
    for i in range(1, s):
        for j in range(i-1, -1, -1):
            if a[j]>a[j+1]:
                a[j+1], a[j] = a[j], a[j+1]
    return a

def test_sort():
    a = range(1, 20)
    random.shuffle(a)
    print a
    print sorted(a)             # examin the test result
    random.shuffle(a)
    print a
    print bubble_sort(a)        # hand implemented result
    random.shuffle(a)
    print a
    print selection_sort(a)
    random.shuffle(a)
    print a
    print insertion_sort(a)

#############################################################################
### the main entry
#############################################################################

def main():
    """
    The main entry of this program (for testing the functions)
    """
    print 'sort:';test_sort()

if __name__ == "__main__":
    main()