func_code: def maximum(lis, p=0):
      if lis == []:
          return p
      n = lis.pop()
      if n > p:
          p = n
      return maximum(lis, p)
annotation: def maximum(lis, p=None):
      if lis == []:
          return p
      n = lis.pop()
      if p == None or n > p:
          p = n
      return maximum(lis, p)
  