As discussed in issue 16468, a metavar may be used to provide an alternative representation of a choices option.  However if a metvar like 'range(20)' is used, usage formatter strips off the '()'.

    >>> parser.add_argument('foo', type=int, 
        choices=range(20), metavar='range(0,20)')
    >>> parser.format_usage()
    # expect: 'usage: PROG [-h] range(0,20)\n'
    # actual: 'usage: PROG [-h] range0,20\n'

This is done by a line in the help formater that removes excess mutually exclusive group notation:

    HelpFormatter._format_actions_usage
       ...
       text = _re.sub(r'\(([^|]*)\)', r'\1', text)

A solution is to change this line to distinguish between a case like ' (...)' and 'range(...)'

    text = _re.sub(r'( )\(([^|]*)\)', r'\1\2', text)

I just posted a patch to http://bugs.python.org/issue16468 that uses (and tests) this fix.

This issue should also preserve a metavar like: '(one)two', i.e. '(' at the start.  

In http://bugs.python.org/issue10984 these _re replacements are applied to individual action strings as well as the whole usage line.  So if () are to be removed from '[-h] (-y)', they should also be removed from '(-y)'.

I just submitted at patch to http://bugs.python.org/issue11874 that takes care of this issue as well.

I rewrote _format_actions_usage() so it formats the parts directly, so there is no need cleanup or parse the full text string.

Reproduced on 3.11:

>>> import argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('foo', type=int, choices=range(20), metavar='range(0,20)')
_StoreAction(option_strings=[], dest='foo', nargs=None, const=None, default=None, type=<class 'int'>, choices=range(0, 20), help=None, metavar='range(0,20)')
>>> parser.format_usage()
'usage: [-h] range0,20\n'