input: Write a function to implement an insertion sort algorithm in Python. The function should sort the input list in ascending order. If the input list is empty, the function should return an empty 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, 4, 1, 2])==[1, 2, 3, 4, 5]
  assert insertion_sort([])==[]
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