code: def get_timezone_string(self, dt=None):
          
          if dt is None:
              download_date = self.meta.get('download_date')
              if download_date:
                  dt = datetime.datetime.strptime(download_date, '%Y-%m-%d')
              else:
                  dt = datetime.datetime.today()
          loc_dt = self._timezone.localize(dt)
          # get the timezone
          timezone_string = loc_dt.strftime("%z")
          return timezone_string
docs: Return the timezone of the GTFS database object as a string.
          The assumed time when the timezone (difference) is computed
          is the download date of the file.
          This might not be optimal in all cases.
  
          So this function should return values like:
              "+0200" or "-1100"
  
          Parameters
          ----------
          dt : datetime.datetime, optional
              The (unlocalized) date when the timezone should be computed.
              Defaults first to download_date, and then to the runtime date.
  
          Returns
          -------
          timezone_string : str