Custom help format for a choice argparse argument

[Weatherby,Gerard]

Why not something like:

        parser.add_argument("-z", "--zone")
       args = parser.parse_args()
       if args.zone and args.zone not in ptyz.all_timezones:
                print(“Invalid timezone”,file=sys.stderr)
                …



From: Python-list <python-list-bounces+gweatherby=uchc.edu at python.org> on behalf of Ivan "Rambius" Ivanov <rambiusparkisanius at gmail.com>
Date: Friday, January 27, 2023 at 3:33 PM
To: Python <python-list at python.org>
Subject: Custom help format for a choice argparse argument
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Hello,

I am developing a script that accepts a time zone as an option. The
time zone can be any from pytz.all_timezones. I have

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("-z", "--zone", choices=pytz.all_timezones)
    args = parser.parse_args()
    print(args)
    print(f"Specified timezone: {args.zone}")

It works, but when I run it with the -h option it dumps all entries in
pytz.all_timezones. I would like to modify the help format for just
-z|--zone option. I read the docs about HelpFormatter and argparse.py
and I ended up with

class CustomHelpFormatter(argparse.HelpFormatter):
    def _metavar_formatter(self, action, default_metavar):
        if action.dest == 'zone':
            result = 'zone from pytz.all_timezones'
            def format(tuple_size):
                if isinstance(result, tuple):
                    return result
                else:
                    return (result, ) * tuple_size
            return format
        else:
            return super(CustomHelpFormatter,
self)._metavar_formatter(action, default_metavar)


def main():
    parser = argparse.ArgumentParser(formatter_class=CustomHelpFormatter)
    parser.add_argument("-z", "--zone", choices=pytz.all_timezones)
    args = parser.parse_args()
    print(args)
    print(f"Specified timezone: {args.zone}")

This works, but is there a more elegant way to achieve it?

Regards
rambius

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