first attempt at a quick sort

readme.md

Written from the explanation here https://www.youtube.com/watch?v=aQiWF4E8flQ

quick_sort.py

def quick_sort(l, start=None, end=None):
    # get the length of our working list
    list_len = len(l[start:end])
    # if this is the first iteration end is length of whole list
    end = len(l) if end is None else end
    # choose the last item of working list as pivot
    pivot = l[end-1]
    # set wall left of first element in working list
    wall_index = start-1 if start is not None else -1
    # set the current element we start with to after wall (first element in working list)
    current_element = l[wall_index+1]
    # count iterations starting with 0 or start with working list start
    count = start if start is not None else 0
    while current_element != pivot:
        if current_element < pivot:
            # swap current element with index just right of the wall
            l[count], l[wall_index + 1] = l[wall_index + 1], l[count]
            # now move the wall
            wall_index += 1
        count += 1
        # move pointer to next element
        current_element = l[count]
    # swap pivot with first element on right side of wall as we know that's its rightful place
    l[end - 1], l[wall_index + 1] = l[wall_index + 1], l[end-1]
    # now pass the left into quick_sort again if we have more than 1 element
    if len(l[start:wall_index + 2]) > 1:
        quick_sort(l, None, wall_index + 1)
    # now pass the right into quick_sort again if we have more than 1 element
    if len(l[wall_index + 1:end]) > 1:
        # note + 2 as we don't want to pass in this iterations pivot as its in correct position
        quick_sort(l, wall_index + 2, None)

if __name__ == '__main__':
    my_list = [1, 12, 4, 7, 3, 5, 2, 6, 11, 10, 9, 13, 8]
    quick_sort(my_list)
    print(my_list)