code: def time_since(self, mtype):
          '''return the time since the last message of type mtype was received'''
          if not mtype in self.messages:
              return time.time() - self.start_time
          return time.time() - self.messages[mtype]._timestamf time_since(self, mtype):
          '''return the time since the last message of type mtype was received'''
          if not mtype in self.messages:
              return time.time() - self.start_time
          return time.time() - self.messages[mtype]._timestamp
docs: return the time since the last message of type mtype was received