input: 
  def insertion_sort(arr):
      """ Sort a list of n distinct integers using the insertion sort algorithm.
      >>> insertion_sort([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5])
      [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9]
      >>> insertion_sort([40, 20, 60, 10, 50, 30])
      [10, 20, 30, 40, 50, 60]
      """
      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 -= 1
          arr[j + 1] = key
  
output:     return arr