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([5,4,3,2,1]) == [1,2,3,4,5]
  assert insertion_sort([1,2,3,4,5]) == [1,2,3,4,5]
  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