Merge sort!

merge_sort.py

def merge(arr, arr_ptr, half, half_ptr):
    while half_ptr < len(half):
        arr[arr_ptr] = half[half_ptr]
        half_ptr = half_ptr + 1
        array_ptr = array_ptr + 1
    return array_ptr

def merge_sort(arr):
    print("Splitting ", arr)
    if len(arr) > 1:
        half_way = len(arr) // 2
        left_half = arr[:half_way]
        right_half = arr[half_way:]
        merge_sort(left_half)
        merge_sort(right_half)
        left_ptr, right_ptr, arr_ptr = 0, 0, 0
        # By the time we make it here, our left and right has been sorted. Woah
        while left_ptr < len(left_half) and right_ptr < len(right_half):
            if left_half[left_ptr] < right_half[right_ptr]:
                arr[arr_ptr] = left_half[left_ptr]
                left_ptr = left_ptr + 1
            else:
                arr[arr_ptr] = right_half[right_ptr]
                right_ptr = right_ptr + 1
            arr_ptr = arr_ptr + 1
        arr_ptr = merge(arr, arr_ptr, left_half, left_ptr)
        merge(arr, arr_ptr, right_half, right_ptr)
    print("Merging", arr)

integer_list = [54, 26, 93, 17, 77, 31, 44, 55, 20]
merge_sort(integer_list)
print(integer_list)