Simple implementation of merge sort in python

merge sort.py

def merge_sort(lst):
    if len(lst) <= 1 :
		return lst
	left = merge_sort(lst[:len(lst)/2])
	right = merge_sort(lst[len(lst)/2:])
	return merge(left, right)

def merge(left, right):
	lst = []
	while len(left) > 0 and len(right) > 0:
		if left[0] >= right[0]:
			lst.append(right.pop(0))
		else:
			lst.append(left.pop(0))
	lst.extend(left)
	lst.extend(right)
	return lst