mergesort.py

def merge_sort(array):

    if len(array) <= 1:
        return array

    midpoint = int(len(array) / 2)

    left, right = merge_sort(array[:midpoint]), merge_sort(array[midpoint:])

    return merge(left, right)


def merge(left, right):
    result = []
    left_pointer = right_pointer = 0

    while left_pointer < len(left) and right_pointer < len(right):
        if left[left_pointer] <= right[right_pointer]:
            result.append(left[left_pointer])
            left_pointer += 1

        elif right[right_pointer] < left[left_pointer]:
            result.append(right[right_pointer])
            right_pointer += 1

    result.extend(left[left_pointer:])
    result.extend(right[right_pointer:])

    return result


# if __name__ == "__main__":
#     array = [5, 4, 3, 2, 1]
#     print(array)
#
#     result = merge_sort(array)
#     print(result)