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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def DisjoinCalendars(self, cutoff):
 """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. """


    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)