code: def time_slice(self, start, end):
          
          if start < self.start_time:
              raise ValueError('Time series does not contain a time as early as %s' % start)
  
          if end > self.end_time:
              raise ValueError('Time series does not contain a time as late as %s' % end)
  
          start_idx = int((start - self.start_time) * self.sample_rate)
          end_idx = int((end - self.start_time) * self.sample_rate)
          return self[start_idx:end_idx]
docs: Return the slice of the time series that contains the time range
          in GPS seconds.