input: Write a function to implement an 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, 1, 2])==[1, 2, 3, 4]
  assert insertion_sort([3, 5, 10, 1, 2])==[1, 2, 3, 5, 10]
  assert insertion_sort([0, -1, 2, -3])==[-3, -1, 0, 2]
  assert insertion_sort([])==[]
  assert insertion_sort([5])==[5]
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