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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 _ParseTimezoneOption(self, options):
 """Parses the timezone options. Args: options (argparse.Namespace):
 command line arguments. Raises: BadConfigOption: if the options are invalid. """

    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