input: Write a function to execute a valid insertion sort on a given list of integers.
  def insertion_sort(arr):
   for i in range(1, len(arr)):
   key = ar
output: r[i]
   j = i - 1
   while j >= 0 and key < arr[j]:
   arr[j + 1] = arr[j]
   j -= 1
   arr[j + 1] = key