input: Write a function to sort a list using the insertion sort algorithm.
  def insertion_sort(list):
      for i in range(1,len(list)):
          key = list[i]
          j = i - 1
          while j>=0 and key < list[j]:
              list[j+1] = list[j]
              j-=1
          list[j+1] = key
      return list
  
  assert insertion_sort([3, 2, 1])==[1, 2, 3]
  assert insertion_sort([5, 3, 4, 1, 2])==[1, 2, 3, 4, 5]
  assert insertion_sort([1, 2, 3])==[1, 2, 3]
  assert insertion_sort([])==[]
  assert insertion_sort([1])==[1]
output: def insertion_sort(list):
      for i in range(1,len(list)):
          key = list[i]
          j = i - 1
          while j>=0 and key < list[j]:
              list[j+1] = list[j]
              j-=1
          list[j+1] = key
      return list