def _format_option_strings(self, option, mvarfmt=' <{}>', optsep=', '):
        """
        Return a comma-separated list of option strings and metavars.

        :param option:  tuple of (short opt, long opt), e.g: ('-f', '--format')
        :param mvarfmt: metavar format string
        :param optsep:  separator
        """
        opts = []

        if option._short_opts:
            opts.append(option._short_opts[0])
        if option._long_opts:
            opts.append(option._long_opts[0])
        if len(opts) > 1:
            opts.insert(1, optsep)

        if option.takes_value():
            metavar = option.metavar or option.dest.lower()
            opts.append(mvarfmt.format(metavar.lower()))

        return ''.join(opts)

        Return a comma-separated list of option strings and metavars.

        :param option:  tuple of (short opt, long opt), e.g: ('-f', '--format')
        :param mvarfmt: metavar format string
        :param optsep:  separator
        
product/gradle-plugin/src/main/python/pip/_internal/cli/parser.py