input: Write a function to implement the insertion sort algorithm in Python. The function should take a list as input and return the sorted list.
  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([4, 3, 2, 10, 12, 1, 5, 6])==[1, 2, 3, 4, 5, 6, 10, 12]
  assert insertion_sort([64, 34, 25, 12, 22, 11, 90])==[11, 12, 22, 25, 34, 64, 90]
  assert insertion_sort([])==[]
  assert insertion_sort([5])==[5]
  assert insertion_sort([3, 7, 4, 9, 5, 2, 6, 1])==[1, 2, 3, 4, 5, 6, 7, 9]
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