Quicksort in Place

quicksort.py

def quicksort(arr,start,stop):
	if stop > start:
		left = start
		right = stop
		pivot = arr[start]
		while left <= right:
			while arr[left] < pivot:
				left += 1
			while arr[right] > pivot:
				right -= 1
			if left <= right:
				arr[left],arr[right] = arr[right],arr[left]
				left += 1
				right -= 1
		quicksort(arr,start,right)
		quicksort(arr,left,stop)
	
arr = [4,2,1,3,5,6]
quicksort(arr,0,len(arr)-1)
print(arr)