`argparse._SubParsersAction.add_parser` should default to `description` matching `help`

Feature or enhancement

Proposal:

import argparse

# create the top-level parser
parser = argparse.ArgumentParser(prog='PROG')
parser.add_argument('--foo', action='store_true', help='foo help')
subparsers = parser.add_subparsers(help='subcommand help')

# create the parser for the "a" command
parser_a = subparsers.add_parser('a', help='a help')
parser_a.add_argument('bar', type=int, help='bar help')

# create the parser for the "b" command
parser_b = subparsers.add_parser('b', help='b help', description='b help')
parser_b.add_argument('--baz', choices=('X', 'Y', 'Z'), help='baz help')

# parse the args
print(parser.parse_args())

This currently produces:

gsnedders@gsnedders-margot tmp.IKpGQE2mE3 % python3.13 test.py --help  
usage: PROG [-h] [--foo] {a,b} ...

positional arguments:
  {a,b}       subcommand help
    a         a help
    b         b help

options:
  -h, --help  show this help message and exit
  --foo       foo help
gsnedders@gsnedders-margot tmp.IKpGQE2mE3 % python3.13 test.py a --help
usage: PROG a [-h] bar

positional arguments:
  bar         bar help

options:
  -h, --help  show this help message and exit
gsnedders@gsnedders-margot tmp.IKpGQE2mE3 % python3.13 test.py b --help
usage: PROG b [-h] [--baz {X,Y,Z}]

b help

options:
  -h, --help     show this help message and exit
  --baz {X,Y,Z}  baz help

It would be nicer, however, if add_parser's description parameter defaulted to the value of the help argument.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

https://github.com/python/cpython/issues/89438 considered not outputting the value of help here to be a bug, but was closed because the description parameter also exists.

Linked PRs

• gh-135236

从 argparse._SubParsersAction.add_parser 开始，查看链接的 PR gh-135236，以了解提议的行为。完成的标准是：子解析器使用其帮助文本作为默认描述，同时显式提供的描述仍然有效，并且相关的 argparse 行为由测试覆盖。