new_contents: import datetime
  from functools import wraps
  
  def timer(func):
      @wraps(func)
      def func_wrapper(*args, **kwargs):
          start_at = datetime.datetime.now()
  
          result = func(*args, **kwargs)
  
          end_at = datetime.datetime.now()
          time_cost = end_at - start_at
          return result , time_cost
      return func_wrapper
  
  
  if __name__ == '__main__':
  
      @timer
      def hello(name):
          return "hello " + name
  
  
      print hello('li')
  
subject: add timer as a decorator