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bpo-29298: Fix crash with required subparsers without dest #3680

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bpo-29298: Fix crash with required subparsers without dest #3680

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bpo-29298: Fix crash with required subparsers without dest
asottile Sep 20, 2017
fd1a8c0
Better demonstrate the error messages produced
asottile Sep 22, 2017
6a09976
Use multiple choices to make output more obvious
asottile Sep 22, 2017
36e8f80
re-add required=True to tests
asottile Jul 20, 2021
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2 Lib/argparse.py
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@@ -727,6 +727,8 @@ def _get_action_name(argument):
return argument.metavar
elif argument.dest not in (None, SUPPRESS):
return argument.dest
elif argument.choices:
return '{' + ','.join(argument.choices) + '}'

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@merwok

merwok Sep 20, 2017
Member

The test doesn’t really help me understand what this change does (i.e. what a human would see in an error case).

I’m also not sure if some of the changes in the various patches for bpo-9253 (especially in tests) could be useful here.

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@asottile

asottile Sep 20, 2017
Author Contributor

I'll check those out. I had a difficult time demonstrating (by assertion) the actual output (didn't find any examples) -- I'll bang against that and hopefully I'll make something more expressive :)

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@asottile

asottile Sep 22, 2017 •
edited
Author Contributor

@merwok looks like they had the same idea I had (but a different implementation) -- I took inspiration from one of their tests for additional coverage and updated the tests to hopefully be more expressive (and have a better failure mode)

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@encukou

encukou May 25, 2018
Member

Code for this is already in _metavar_formatter:

        elif action.choices is not None:
            choice_strs = [str(choice) for choice in action.choices]
            result = '{%s}' % ','.join(choice_strs)

The metavar formatter can be called, if the parser is known (as self), using:

            default = self._get_default_metavar_for_positional(action)
            metavar, = self._metavar_formatter(action, default)(1)

Perhaps _get_action_name should be made into a method, or take the parser as an optional argument?
else:
return None

24 Lib/test/test_argparse.py
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@@ -2060,6 +2060,30 @@ def test_required_subparsers_default(self):
ret = parser.parse_args(())
self.assertIsNone(ret.command)

def test_required_subparsers_no_destination_error(self):
parser = ErrorRaisingArgumentParser()
subparsers = parser.add_subparsers(required=True)
subparsers.add_parser('foo')
subparsers.add_parser('bar')
with self.assertRaises(ArgumentParserError) as excinfo:
parser.parse_args(())
self.assertRegex(
excinfo.exception.stderr,
'error: the following arguments are required: {foo,bar}\n$'

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@serhiy-storchaka

serhiy-storchaka May 11, 2018
Member

Add a space after comma. Why braces are used?

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@merwok

merwok May 11, 2018
Member

I think this is a notation for alternatives: it means one of foo or bar is required.

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@asottile

asottile May 11, 2018
Author Contributor

This is consistent with the rendering of choices:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--foo', choices=('baz', 'womp'))
parser.parse_args()
$ python test.py --help
usage: test.py [-h] [--foo {baz,womp}]

optional arguments:
  -h, --help        show this help message and exit
  --foo {baz,womp}
)

def test_wrong_argument_subparsers_no_destination_error(self):
parser = ErrorRaisingArgumentParser()
subparsers = parser.add_subparsers(required=True)
subparsers.add_parser('foo')
subparsers.add_parser('bar')
with self.assertRaises(ArgumentParserError) as excinfo:
parser.parse_args(('baz',))
self.assertRegex(
excinfo.exception.stderr,
r"error: argument {foo,bar}: invalid choice: 'baz' \(choose from 'foo', 'bar'\)\n$"

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@serhiy-storchaka

serhiy-storchaka May 11, 2018
Member

"foo, bar" is duplicated. And this error message looks confusing to me. What it means?

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@asottile

asottile May 11, 2018
Author Contributor

yeah I didn't really know what to do for this, it's essentially an anonymous positional choices argument. Personally I'd love a default dest='command' but I imagine that could cause some incompatibility?

Then this would read something like error: argument command: invalid choice ...
)

def test_optional_subparsers(self):
parser = ErrorRaisingArgumentParser()
subparsers = parser.add_subparsers(dest='command', required=False)
2 Misc/NEWS.d/next/Library/2017-09-20-14-43-03.bpo-29298._78CSN.rst
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@@ -0,0 +1,2 @@
Fix ``TypeError`` when required subparsers without ``dest`` do not receive
arguments. Patch by Anthony Sottile.