code: def append(self, event, category=None):
          
          date = datetime.datetime.now()
          self.store.insert(0, (date, event, category))
          if len(self.store) > self.size:
              del self.store[-1]
docs: Adds a new event to the trace store.
          The event may hava a category
  
          Args:
            event (spade.message.Message): the event to be stored
            category (str, optional): a category to classify the event (Default value = None)