Merge sort in Python

merge_sort.py

def merge_sort(lst):
    """
    Performs in-place sorting using the merge sort algorithm
    """
    if len(lst) > 1:
        mid = len(lst) // 2
        left = lst[:mid]
        right = lst[mid:]

        merge_sort(left)
        merge_sort(right)

        i = 0 # left iterator
        j = 0 # right iterator
        k = 0 # dest iterator
        while i < len(left) and j < len(right):
            if left[i] < right[j]:
                lst[k] = left[i]
                i += 1
            else:
                lst[k] = right[j]
                j += 1
            k += 1

        while i < len(left):
            lst[k] = left[i]
            i += 1
            k += 1

        while j < len(right):
            lst[k] = right[j]
            j += 1
            k += 1

lst = [4,5,7,8,3,2,1,8,9,3]
merge_sort(lst)
print(lst) # [1, 2, 3, 3, 4, 5, 7, 8, 8, 9]