input: 
  from typing import List
  
  def insertion_sort(arr: List[int]) -> List[int]:
      """ Sorts a list of n distinct integers using the insertion sort algorithm.
      >>> insertion_sort([4, 2, 7, 1, 9])
      [1, 2, 4, 7, 9]
      >>> insertion_sort([6, 3, 5, 8, 2])
      [2, 3, 5, 6, 8]
      >>> insertion_sort([1])
      [1]
      """
      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
      return arr
  
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 -= 1
          arr[j + 1] = key
      return arr