bpo-38956: remove default option from help string in argparse

[michiboo]

Signed-off-by: Micky Yun Chan (michiboo): [email protected]

https://bugs.python.org/issue38956

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[michiboo]

I already signed the CLA yesterday

[shihai1991]

@michiboo Thanks for your contribute.
just an small advice: pls adding a unit test to against this scenario(Looks adding test case from the bpo-38956 in https://github.com/python/cpython/blob/master/Lib/test/test_argparse.py#L4182 is good enough)

[michiboo]

Hi, I updated the test

[shihai1991]

@michiboo Thanks.
@rhettinger Hi, raymond. I checked that https://github.com/python/cpython/blob/master/Lib/argparse.py#L697 is conflict with https://github.com/python/cpython/blob/master/Lib/argparse.py#L876, so removing the redundant code is fine to me. Pls review this PR if your have free time. Thank you.

[shihai1991]

LGTM now, thanks.

[michiboo]

bump

[rhettinger]

I think the effect of this edit is too broad. Instead, focus on making sure the default only prints once when the formatter_class is set to ArgumentDefaultsHelpFormatter. When formatter_class isn't set, the default still needs to be shown.

Given this script:

from argparse import *

parser = ArgumentParser()
parser.add_argument("--foo", action=BooleanOptionalAction, help="Whether to foo it", default=False)
parser.add_argument("--quux", help="Set the quux", default=42)
print(parser.parse_args())

We still want this output:

$ py tmp.py --help
usage: tmp.py [-h] [--foo | --no-foo] [--quux QUUX]

optional arguments:
  -h, --help       show this help message and exit
  --foo, --no-foo  Whether to foo it (default: False)
  --quux QUUX      Set the quux

[michiboo]

I have made the requested changes; please review again

Hi I have updated the code in add action function since it is not possible to get formatter class in action object, ArgumentDefaultsHelpFormatter already add default value and that was the origin problem which result in duplicate default value in the help string. Now with the default formatter class it can also show the default value.

[abadger]

Hey @rhettinger could you speak on why the default should be displayed for BooleanOptionalArgument out-of-the-box whereas all other shipped actions require setting formatter_class=ArgumentDefaultsHelpFormatter? I do find that showing the default value is useful but it seems to break the expected separation of responsibility between action and formatter.

I ask about this since I have a different bug which would be fixed if BooleanOptionalArgument were to no longer try to add defaults on its own. If BooleanOptionalArgument should continue to do that formatting, though, I could extract the code from ArgumentDefaultsHelpFormatter and have both ArgumentDefaultsHelpFormatter and BooleanOptionalArgument use it which would likely fix my issue, this issue, and a similar class of issues that we just haven't encountered yet.

[rhettinger]

Make sure the default still shown when a formatter_class isn't specified.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[michiboo]

I have made the requested changes; please review again

[bedevere-bot]

Thanks for making the requested changes!

@rhettinger: please review the changes made to this pull request.

[michiboo]

bump

[ambv]

Closing in favor of GH-27672.