quick sort implemented in python

QuickSort.py

#!/usr/bin/python

import random

def quick_sort_(buf, left, right):
    ll, rr = left, right
    pivot = random.choice(buf[left : right + 1])
    while left <= right:
        while buf[left] < pivot:
            left += 1
        while buf[right] > pivot:
            right -= 1
        if left <= right:
            buf[left], buf[right] = buf[right], buf[left]
            left += 1
            right -= 1
    if right > ll:
        quick_sort_(buf, ll, right)
    if left < rr:
        quick_sort_(buf, left, rr)

def quick_sort(buf):
    quick_sort_(buf, 0, len(buf) - 1)

def main():
    buf = [10, 9, 8, 7, 6, 20, 18, 16, 14, 12, 10]
    quick_sort(buf)
    print buf

if __name__ == '__main__':
    main()