input: Write a function to implement an insertion sort algorithm in Python for sorting a list of integers in ascending order. If the input list is empty, return the input list as it is.
  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([5, 2, 9, 1, 5, 6])==[1, 2, 5, 5, 6, 9]
  assert insertion_sort([3, 8, 2, 1, 5])==[1, 2, 3, 5, 8]
  assert insertion_sort([])==[]
  assert insertion_sort([1])==[1]
  assert insertion_sort([4, 3, 2, 1])==[1, 2, 3, 4]
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