[issue31360] argparse mutually_exclusive_group under add_argument_group fails if part of parent_processor

[Paul Traina (discontent)]

New submission from Paul Traina (discontent):

Hopefully I'm not being obtuse, but I seem to be getting incorrect/unexpected help output when using mutually_exclusive_group under an add_argument_group if this layering is happening in a parent parser.

Here's an example of the triggering usage:

import argparse

global_options = argparse.ArgumentParser(add_help=False)
global_options.add_argument('--summary', action='store_true', help='summarize information')
global_options.add_argument('--verbose', action='store_true', help='tell us more')

output_format = global_options.add_argument_group("Output format", "ways to foo")
styles = output_format.add_mutually_exclusive_group()
styles.add_argument('--plain', dest='style')
styles.add_argument('--green', dest='style')
styles.add_argument('--blue', dest='style')

parser = argparse.ArgumentParser()
commands = parser.add_subparsers()
hit = commands.add_parser('hit', parents=[global_options])
miss = commands.add_parser('miss', parents=[global_options])

print(parser.parse_args(['hit', '-h']))

which produces:

usage: bar.py hit [-h] [--summary] [--verbose]
                  [--plain STYLE | --green STYLE | --blue STYLE]

optional arguments:
  -h, --help     show this help message and exit
  --summary      summarize information
  --verbose      tell us more
  --plain STYLE
  --green STYLE
  --blue STYLE

Output format:
  ways to foo


"--plain" "--green" and "--blue" *should* be under "Output format"

----------
components: Library (Lib)
messages: 301437
nosy: Paul Traina (discontent)
priority: normal
severity: normal
status: open
title: argparse mutually_exclusive_group under add_argument_group fails if part of parent_processor
type: behavior
versions: Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue31360>
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