def format_option_strings(self, option):
        """Return a comma-separated list of option strings & metavariables."""
        if option.takes_value():
            metavar = option.metavar or option.dest.upper()
            short_opts = [self._short_opt_fmt % (sopt, metavar)
                          for sopt in option._short_opts]
            long_opts = [self._long_opt_fmt % (lopt, metavar)
                         for lopt in option._long_opts]
        else:
            short_opts = option._short_opts
            long_opts = option._long_opts

        if self.short_first:
            opts = short_opts + long_opts
        else:
            opts = long_opts + short_opts

        return ", ".join(opts)