argparse usage should preserve () in metavars such as range(20)

[paulj3]

BPO	18349
Nosy	@iritkatriel
Files	metaparen.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2013-07-03.06:16:51.100>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = 'argparse usage should preserve () in metavars such as range(20)'
updated_at = <Date 2021-12-10.15:48:45.716>
user = 'https://bugs.python.org/paulj3'

bugs.python.org fields:

activity = <Date 2021-12-10.15:48:45.716>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2013-07-03.06:16:51.100>
creator = 'paul.j3'
dependencies = []
files = ['30754']
hgrepos = []
issue_num = 18349
keywords = ['patch']
message_count = 5.0
messages = ['192222', '192717', '193077', '193188', '408214']
nosy_count = 2.0
nosy_names = ['paul.j3', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue18349'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[paulj3]

As discussed in bpo-16468, a metavar may be used to provide an alternative representation of a choices option. However if a metvar like 'range(20)' is used, usage formatter strips off the '()'.

    >>> parser.add_argument('foo', type=int, 
        choices=range(20), metavar='range(0,20)')
    >>> parser.format_usage()
    # expect: 'usage: PROG [-h] range(0,20)\n'
    # actual: 'usage: PROG [-h] range0,20\n'

This is done by a line in the help formater that removes excess mutually exclusive group notation:

HelpFormatter._format_actions_usage
   ...
   text = _re.sub(r'\(([^|]*)\)', r'\1', text)

A solution is to change this line to distinguish between a case like ' (...)' and 'range(...)'

    text = _re.sub(r'( )\(([^|]*)\)', r'\1\2', text)

[paulj3]

I just posted a patch to http://bugs.python.org/issue16468 that uses (and tests) this fix.

[paulj3]

This issue should also preserve a metavar like: '(one)two', i.e. '(' at the start.

In http://bugs.python.org/issue10984 these _re replacements are applied to individual action strings as well as the whole usage line. So if () are to be removed from '[-h] (-y)', they should also be removed from '(-y)'.

[paulj3]

I just submitted at patch to http://bugs.python.org/issue11874 that takes care of this issue as well.

I rewrote _format_actions_usage() so it formats the parts directly, so there is no need cleanup or parse the full text string.

[iritkatriel]

Reproduced on 3.11:

>>> import argparse
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('foo', type=int, choices=range(20), metavar='range(0,20)')
_StoreAction(option_strings=[], dest='foo', nargs=None, const=None, default=None, type=<class 'int'>, choices=range(0, 20), help=None, metavar='range(0,20)')
>>> parser.format_usage()
'usage: [-h] range0,20\n'

[encukou]

This was fixed in #102318.