code: def _ParseTimezoneOption(self, options):
      
      time_zone_string = self.ParseStringOption(options, 'timezone')
      if isinstance(time_zone_string, py2to3.STRING_TYPES):
        if time_zone_string.lower() == 'list':
          self.list_timezones = True
  
        elif time_zone_string:
          try:
            pytz.timezone(time_zone_string)
          except pytz.UnknownTimeZoneError:
            raise errors.BadConfigOption(
                'Unknown time zone: {0:s}'.format(time_zone_string))
  
          self._preferred_time_zone = time_zone_string
docs: Parses the timezone options.
  
      Args:
        options (argparse.Namespace): command line arguments.
  
      Raises:
        BadConfigOption: if the options are invalid.