def _format_option_strings(self, option, mvarfmt='<STR_LIT>', optsep='<STR_LIT:U+002CU+0020>'):
opts = []<EOL>if option._short_opts:<EOL><INDENT>opts.append(option._short_opts[<NUM_LIT:0>])<EOL><DEDENT>if option._long_opts:<EOL><INDENT>opts.append(option._long_opts[<NUM_LIT:0>])<EOL><DEDENT>if len(opts) > <NUM_LIT:1>:<EOL><INDENT>opts.insert(<NUM_LIT:1>, optsep)<EOL><DEDENT>if option.takes_value():<EOL><INDENT>metavar = option.metavar or option.dest.lower()<EOL>opts.append(mvarfmt % metavar.lower())<EOL><DEDENT>return '<STR_LIT>'.join(opts)<EOL>
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 - evaluated as mvarfmt % metavar
:param optsep:  separator