code: def open(cls, rootdir, end_session=None):
          
          metadata = BcolzMinuteBarMetadata.read(rootdir)
          return BcolzMinuteBarWriter(
              rootdir,
              metadata.calendar,
              metadata.start_session,
              end_session if end_session is not None else metadata.end_session,
              metadata.minutes_per_day,
              metadata.default_ohlc_ratio,
              metadata.ohlc_ratios_per_sid,
              write_metadata=end_session is not None
          )
docs: Open an existing ``rootdir`` for writing.
  
          Parameters
          ----------
          end_session : Timestamp (optional)
              When appending, the intended new ``end_session``.