code: def _special_dates(self, calendars, ad_hoc_dates, start_date, end_date):
          
          # List of Series for regularly-scheduled times.
          regular = [
              scheduled_special_times(
                  calendar,
                  start_date,
                  end_date,
                  time_,
                  self.tz,
              )
              for time_, calendar in calendars
          ]
  
          # List of Series for ad-hoc times.
          ad_hoc = [
              pd.Series(
                  index=pd.to_datetime(datetimes, utc=True),
                  data=days_at_time(datetimes, time_, self.tz),
              )
              for time_, datetimes in ad_hoc_dates
          ]
  
          merged = regular + ad_hoc
          if not merged:
              # Concat barfs if the input has length 0.
              return pd.Series([])
  
          result = pd.concat(merged).sort_index()
          return result.loc[(result >= start_date) & (result <= end_date)]
docs: Compute a Series of times associated with special dates.
  
          Parameters
          ----------
          holiday_calendars : list[(datetime.time, HolidayCalendar)]
              Pairs of time and calendar describing when that time occurs. These
              are used to describe regularly-scheduled late opens or early
              closes.
          ad_hoc_dates : list[(datetime.time, list[pd.Timestamp])]
              Pairs of time and list of dates associated with the given times.
              These are used to describe late opens or early closes that occurred
              for unscheduled or otherwise irregular reasons.
          start_date : pd.Timestamp
              Start of the range for which we should calculate special dates.
          end_date : pd.Timestamp
              End of the range for which we should calculate special dates.
  
          Returns
          -------
          special_dates : pd.Series
              Series mapping trading sessions with special opens/closes to the
              special open/close for that session.