Bug report

Using ArgumentDefaultsHelpFormatter as formatter_class of ArgumentParser doesn't always shows default even if the default for argument is set. It's expected to show default if provided.

Example:

    parser = ArgumentParser(formatter_class=ArgumentDefaultsHelpFormatter)
    parser.add_argument('foo', default=1)
    parser.add_argument('bar', nargs='*', default=1)
    parser.add_argument('baz', nargs='*', default=1, help='baz help')
    parser.add_argument('-a', default=1)
    parser.add_argument('-b', default=1, help='b_help')
    parser.print_help()

provides

positional arguments:
  foo
  bar
  baz         baz help (default: 1)

options:
  -h, --help  show this help message and exit
  -a A
  -b B        b_help (default: 1)

Though I see no reason to not show default for -a, foo and bar.
Making help argument mandatory to show default is necessary imho, but what is really strange is that it's enough for an option, but requires nargs for a positional argument.

Your environment

• CPython versions tested on: 3.10.5
• Operating system and architecture: Arch Linux x86_64 5.15.55-1-lts

Linked PRs

• gh-95889: Implement Default Value Display in ArgumentsDefaultsHelpFormatter Help Message #112682