Custom help format for a choice argparse argument
Peter Otten
__peter__ at web.de
Mon Jan 30 17:20:26 EST 2023
On 27/01/2023 21:31, Ivan "Rambius" Ivanov wrote:
> 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?
It may be sufficient to specify a metavar:
>>> import argparse
>>> p = argparse.ArgumentParser()
>>> p.add_argument("--foo", choices="alpha beta gamma".split(),
metavar="<any greek letter>")
[...]
>>> p.parse_args(["-h"])
usage: [-h] [--foo <any greek letter>]
optional arguments:
-h, --help show this help message and exit
--foo <any greek letter>
While that helps with --help it doesn't always prevent the choices list
from being spelt out:
>>> p.parse_args(["--foo", "whatever"])
usage: [-h] [--foo <any greek letter>]
: error: argument --foo: invalid choice: 'whatever' (choose from
'alpha', 'beta', 'gamma')
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