def merge_sort(array):
    if len(array) == 1:
        return array
    _________________________
    return merge(left, right)

def merge(left, right):
    left_index, right_index, merge_array = 0, 0, list()
    while left_index < len(left) and right_index < len(right):
        if left[left_index] <= right[right_index]:
            merge_array.append(left[left_index])
            left_index += 1
        else:
            merge_array.append(right[right_index])
            right_index += 1
    merge_array = merge_array + left[left_index:] + right[right_index:]
    return merge_array