A few sorting algorithms in Python

sorting.py

import math
import random

#-------------------------------------------------------------------------------

'''
Default comparator that sorts
numeric values in their natural order.
'''
def comparator(one, two):
    return one - two

#-------------------------------------------------------------------------------

'''
Comparator that sorts numeric
values in descending order.
'''
def reverse(one, two):
    return two - one

#-------------------------------------------------------------------------------

'''
Sorts an array of values with a specified comparator.
'''
def msort(array, comparator=comparator):
    mergesort(array, 0, len(array)-1, comparator)

#-------------------------------------------------------------------------------

'''
Merge sort on a sub-array.
'''
def mergesort(a, lo, hi, compare=comparator):

    if lo < hi:

        mid = math.floor(lo + (hi - lo) / 2)

        mergesort(a, lo, mid, compare)
        mergesort(a, mid+1, hi, compare)

        i = lo
        j = mid+1
        k = lo
        b = [None] * (len(a) * 2)

        while i <= mid and j <= hi:

            if compare(a[i], a[j]) < 0:

                b[k] = a[i]
                i   += 1

            else:

                b[k] = a[j]
                j   += 1

            k += 1

        while i <= mid:

            b[k] = a[i]
            k   += 1
            i   += 1

        while j <= hi:

            b[k] = a[j]
            k   += 1
            j   += 1

        for m in range(lo, k):
            a[m] = b[m]

#-------------------------------------------------------------------------------

'''
Sorts an array of values with a specified comparator.
'''
def qsort(array, comparator=comparator):

    quicksort(array, 0, len(array)-1, comparator)

    return array

#-------------------------------------------------------------------------------

'''
Quicksort using Hoare partitioning scheme.
'''
def quicksort(a, lo, hi, compare=comparator):

    if lo >= hi:
        return

    i = lo
    j = hi
    r = random.randint(lo, hi - 1)

    pivot = a[r];

    while i <= j:

        while compare(a[i], pivot) < 0:
            i += 1

        while compare(a[j], pivot) > 0:
            j -= 1

        if i <= j:

            t    = a[i]
            a[i] = a[j]
            a[j] = t

            i += 1
            j -= 1

        if lo < j:
            quicksort(a, lo, j, compare)

        if i < hi:
            quicksort(a, i, hi, compare)

#-------------------------------------------------------------------------------

'''
Selection sort with an optional comparator.
'''
def ssort(a, compare=comparator):

    n = len(a)

    for i in range(0, n):
        min = i

        for j in range(i, n):

            if compare(a[j], a[min]) < 0:

                min = j

        if min != i:

            t      = a[i]
            a[i]   = a[min]
            a[min] = t

    return a