[issue45580] argparse.ArgumentParser.add_mutually_exclusive_group : metavar create parenthesis undefined behavior

[paul j3]

paul j3  added the comment:

The usage formatting is fragile, with many associated bug reports.  Until 
someone does a major rewrite, it is best to avoid special characters, 
especially `()` and `[]` in the `dest` or `metavar`.

Usage uses () to encolde mutually_exclusive_groups and [] to mark non-required 
arguments.  Don't confuse your users (or argparse) with other uses of these 
characters.

--
nosy: +paul.j3

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[issue45580] argparse.ArgumentParser.add_mutually_exclusive_group : metavar create parenthesis undefined behavior

[Nikita Sobolev]

Nikita Sobolev  added the comment:

Maybe instead we can show users something like:

```
usage: ex.py [-h] (-p '/var/www/html' | -r 'http)s(://Host:Port') [--last-args 
LAST_ARGS]
```

?

--
components: +Library (Lib) -Parser
type:  -> behavior
versions: +Python 3.10, Python 3.11

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[issue45580] argparse.ArgumentParser.add_mutually_exclusive_group : metavar create parenthesis undefined behavior

[Nikita Sobolev]

Nikita Sobolev  added the comment:

I confirm this happens on all recent Python versions.

The source of this problem is that `argparse` uses `regex` module to replace 
some substrings. Direct link: 
https://github.com/python/cpython/blame/8ce20bbdd6d2b1277a5e74154fcdcef2cb0fee49/Lib/argparse.py#L487

Quick debug showed that without this line these tests fail:

```
==
FAIL: test_help_when_required 
(test.test_argparse.TestMutuallyExclusiveFirstSuppressed)
--
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2649, 
in test_help_when_required
self.assertEqual(format_help(), textwrap.dedent(help))
^^
AssertionError: 'usage: PROG [-h] (-y)\n\noptions:\n  -h, --help  show this[42 
chars]lp\n' != 'usage: PROG [-h] -y\n\noptions:\n  -h, --help  show this h[40 
chars]lp\n'
- usage: PROG [-h] (-y)
?  -  -
+ usage: PROG [-h] -y
  
  options:
-h, --help  show this help message and exit
-y  y help


==
FAIL: test_usage_when_required 
(test.test_argparse.TestMutuallyExclusiveFirstSuppressed)
--
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2639, 
in test_usage_when_required
self.assertEqual(format_usage(), textwrap.dedent(expected_usage))
^
AssertionError: 'usage: PROG [-h] (-y)\n' != 'usage: PROG [-h] -y\n'
- usage: PROG [-h] (-y)
?  -  -
+ usage: PROG [-h] -y


==
FAIL: test_help_when_required 
(test.test_argparse.TestMutuallyExclusiveFirstSuppressedParent)
--
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2649, 
in test_help_when_required
self.assertEqual(format_help(), textwrap.dedent(help))
^^
AssertionError: 'usage: PROG [-h] (-y)\n\noptions:\n  -h, --help  show this[42 
chars]lp\n' != 'usage: PROG [-h] -y\n\noptions:\n  -h, --help  show this h[40 
chars]lp\n'
- usage: PROG [-h] (-y)
?  -  -
+ usage: PROG [-h] -y
  
  options:
-h, --help  show this help message and exit
-y  y help


==
FAIL: test_usage_when_required 
(test.test_argparse.TestMutuallyExclusiveFirstSuppressedParent)
--
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_argparse.py", line 2639, 
in test_usage_when_required
self.assertEqual(format_usage(), textwrap.dedent(expected_usage))
^
AssertionError: 'usage: PROG [-h] (-y)\n' != 'usage: PROG [-h] -y\n'
- usage: PROG [-h] (-y)
?  -  -
+ usage: PROG [-h] -y


--
Ran 1672 tests in 23.258s

FAILED (failures=4)
test test_argparse failed
test_argparse failed (4 failures)

== Tests result: FAILURE ==

1 test failed:
test_argparse

Total duration: 25.6 sec
Tests result: FAILURE
```

--
nosy: +sobolevn

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[issue45580] argparse.ArgumentParser.add_mutually_exclusive_group : metavar create parenthesis undefined behavior

[AbcSxyZ]

New submission from AbcSxyZ :

Hi,

I'm getting a kind of undefined behavior where parenthesis seem handled in a 
strange way. On display, it has a conflict between parenthesis of the option, 
and nested parenthesis within a metavar.

## Reproduction script

```
import argparse

def main():
parser = argparse.ArgumentParser()

group = parser.add_mutually_exclusive_group(required=True)

group.add_argument("-p", "--path", metavar="/var/www/html", 
help="DocumentRoot path")
group.add_argument("-r", "--reverse", metavar="http)s(://Host:Port",
help="Reverse proxy address")

parser.add_argument("--last-args")
return parser.parse_args()

main()
```

## Output of help menu
```
usage: crash.py [-h] (-p /var/www/html | -r http)s://Host:Port [--last-args 
LAST_ARGS]
```

## Expected behavior
```
usage: crash.py [-h] (-p /var/www/html | -r http)s(://Host:Port) [--last-args 
LAST_ARGS]
```

--
components: Parser
messages: 404815
nosy: AbcSxyZ, lys.nikolaou, pablogsal
priority: normal
severity: normal
status: open
title: argparse.ArgumentParser.add_mutually_exclusive_group : metavar create 
parenthesis undefined behavior
versions: Python 3.9

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