input: Write a function to execute a valid insertion sort on a given list of integers. If the given list is empty, return the empty list.
  def insertion_sort(arr):
   if len(arr) == 0:
   return 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
  
  assert insertion_sort([4, 3, 2, 10, 12, 1, 5, 6]) == [1, 2, 3, 4, 5, 6, 10, 12]
  assert insertion_sort([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
  assert insertion_sort([5, 3, 8, 4, 6]) == [3, 4, 5, 6, 8]
  assert insertion_sort([]) == []
output: def insertion_sort(arr):
      if len(arr) == 0:
          return 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