input: def insertion_sort(list):
      """Sort a given list using insertion sort algorithm.
      >>> insertion_sort([3, 2, 1, 4])
      [1, 2, 3, 4]
      >>> insertion_sort([5, 7, 4, 6, 3, 2, 1])
      [1, 2, 3, 4, 5, 6, 7]
      """
      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
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