code: def DisjoinCalendars(self, cutoff):
      
  
      def TruncatePeriod(service_period, start, end):
        """Truncate the service period to into the range [start, end].
  
        Args:
          service_period: The service period to truncate.
          start: The start date as a string in YYYYMMDD format.
          end: The end date as a string in YYYYMMDD format.
        """
        service_period.start_date = max(service_period.start_date, start)
        service_period.end_date = min(service_period.end_date, end)
        dates_to_delete = []
        for k in service_period.date_exceptions:
          if (k < start) or (k > end):
            dates_to_delete.append(k)
        for k in dates_to_delete:
          del service_period.date_exceptions[k]
  
      # find the date one day before cutoff
      year = int(cutoff[:4])
      month = int(cutoff[4:6])
      day = int(cutoff[6:8])
      cutoff_date = datetime.date(year, month, day)
      one_day_delta = datetime.timedelta(days=1)
      before = (cutoff_date - one_day_delta).strftime('%Y%m%d')
  
      for a in self.feed_merger.a_schedule.GetServicePeriodList():
        TruncatePeriod(a, 0, before)
      for b in self.feed_merger.b_schedule.GetServicePeriodList():
        TruncatePeriod(b, cutoff, '9'*8)
docs: Forces the old and new calendars to be disjoint about a cutoff date.
  
      This truncates the service periods of the old schedule so that service
      stops one day before the given cutoff date and truncates the new schedule
      so that service only begins on the cutoff date.
  
      Args:
        cutoff: The cutoff date as a string in YYYYMMDD format. The timezone
                is the same as used in the calendar.txt file.