Visualizing quicksort in python

qsort.py

from pylab import *
from random import shuffle

def qsort(l, s, e):
    if s < e:
        mid = part(l, s, e)
        qsort(l, s, mid-1)
        qsort(l, mid+1, e)
    else:
        return

def part(l, s, e):
    pivot = l[e]
    end = s-1
    start = e
    sorted = 0
    while not sorted:
        while not sorted:
            end = end+1
            if end == start:
                sorted = 1
                break

            if l[end] > pivot:
                l[start] = l[end]
                line.set_ydata(u)
                draw()
                break

        while not sorted:
            start = start-1
            if start == end:
                sorted = 1
                break

            if l[start] < pivot:
                l[end] = l[start]
                line.set_ydata(u)
                draw()
                break
    l[start] = pivot
    line.set_ydata(u)
    draw()
    return start

if __name__ == "__main__":
    ion()
    u = range(300)
    shuffle(u)
    line, = plot(range(300), u, 'r.')
    qsort(u, 0, len(u)-1)