code: def tick(self):
          
          now = datetime.datetime.now()
          self.add(now)
  
          # Create a list of timestamps, one for each period and
          # representing the beginning of that period (i.e. since now.)
          tstamps = [now - datetime.timedelta(seconds=xx)
                     for xx in self._periods]
  
          # Trim off any tick values older than the earliest timestamp.
          self.removeLT(min(tstamps))
  
          # Create a list of counts, one for each period and
          # representing the number of ticks in that period.
          counts = [self.getCountGT(xx) for xx in tstamps]
  
          # Compute a list of rates for the periods.
          rates = [float(xx)/yy for xx, yy in zip(counts, self._periods)]
  
          # Return the rates as a tuple.
          return tuple(rates)
docs: Tick the ticker.
          Return a tuple of values corresponding to periods given in initializer,
          each value representing the rate of ticks (number of ticks per second)
          during that period.