input: def insertion_sort(arr):
      for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j = j - 1
          arr[j + 1] = key
      return arr
  
  """ 
  >>> insertion_sort([5, 3, 8, 6, 7, 2])
  [2, 3, 5, 6, 7, 8]
  >>> insertion_sort([12, 11, 13, 5, 6])
  [5, 6, 11, 12, 13]
  """
output:     for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j = j - 1
          arr[j + 1] = key
      return arr