input: def insertion_sort(list: list) -> list:
      """
      Sorts a given list using the insertion sort algorithm.
      >>> insertion_sort([4, 2, 7, 1, 3])
      [1, 2, 3, 4, 7]
      >>> insertion_sort([9, 8, 7, 6, 5])
      [5, 6, 7, 8, 9]
      >>> insertion_sort([])
      []
      >>> insertion_sort([1, 2, 3, 4, 5])
      [1, 2, 3, 4, 5]
      """
output:     for i in range(1, len(list)):
          key = list[i]
          j = i - 1
          while j >= 0 and key < list[j]:
              list[j + 1] = list[j]
              j -= 1
          list[j + 1] = key
      return list