[issue17218] support title and description in argparse add_mutually_exclusive_group

[Barry A. Warsaw]

Changes by Barry A. Warsaw :


--
nosy: +barry

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[paul j3]

paul j3 added the comment:

oops - one more glitch (revealed by TestMutuallyExclusiveInGroup):

'add_mutually_exclusive_group' accepts a 'required' argument, but 
'add_argument_group' does not.  So 'add_titled_mutually_exclusive_group' needs 
to be changed to temporarily remove that argument (if given).

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[paul j3]

paul j3 added the comment:

The idea of nesting a mutually_exclusive_group in a titled argument_group is 
already present in `test_argparse.py`.

class TestMutuallyExclusiveInGroup(MEMixin, TestCase):

def get_parser(self, required=None):
parser = ErrorRaisingArgumentParser(prog='PROG')
titled_group = parser.add_argument_group(
title='Titled group', description='Group description')
mutex_group = \
titled_group.add_mutually_exclusive_group(required=required)
mutex_group.add_argument('--bar', help='bar help')
mutex_group.add_argument('--baz', help='baz help')
return parser

failures = ['--bar X --baz Y', '--baz X --bar Y']
successes = [
('--bar X', NS(bar='X', baz=None)),
('--baz Y', NS(bar=None, baz='Y')),
]
successes_when_not_required = [
('', NS(bar=None, baz=None)),
]

usage_when_not_required = '''\
usage: PROG [-h] [--bar BAR | --baz BAZ]
'''
usage_when_required = '''\
usage: PROG [-h] (--bar BAR | --baz BAZ)
'''
help = '''\

optional arguments:
  -h, --help  show this help message and exit

Titled group:
  Group description

  --bar BAR   bar help
  --baz BAZ   baz help
'''
 
So now the question is - do we to modify `add_mutually_exclusive_group` to 
streamline this task?  An alternative is to add a note to the documentation, eg.

Note that currently mutually exclusive argument groups do not 
support the title and description arguments of add_argument_group().
However a such a group can be added to a titled argument group.
(and then add an example)

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[paul j3]

paul j3 added the comment:

The attached file implements a solution using a subclassed ArgumentParser and a 
.add_titled_mutually_exclusive_group method (two versions).

I changed the test conditions a bit, removing a blank line, and making the 
usage 'exclusive'.

--
Added file: http://bugs.python.org/file34926/test_argparse_mutex_with_title1.py

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[paul j3]

paul j3 added the comment:

Using a mutually_exclusive_group is a little more complicated than I implied in 
the previous post.

p=argparse.ArgumentParser()
g=p.add_mutually_exclusive_group()
# currently the code objects to 'title' and 'description' keywords
g.add_argument('--foo')
g.add_argument('--bar')
# but a title can be added after creation
g.title='test'
g.description='description'
# now add the group to the list that is used for help formatting
p._action_groups.append(g)
p.print_help()

producing:

usage: ipython [-h] [--foo FOO | --bar BAR]
optional arguments:
  -h, --help  show this help message and exit
  --foo FOO
  --bar BAR
test:
  description
  --foo FOO
  --bar BAR

Now the arguments appear in both the 'optional arguments' group (a default 
one), and the new group.  That's not what we want.

So the mutually_exclusive_group has to be changed so it accepts title and 
description.  And it also has to block the addition of arguments to one of the 
existing groups.

A key difference is in how _add_action is implemented for the 2 group classes:

For argument_group:

def _add_action(self, action):
action = super(_ArgumentGroup, self)._add_action(action)
self._group_actions.append(action)
return action

for mutually exclusive group

def _add_action(self, action):
...
action = self._container._add_action(action)
self._group_actions.append(action)
return action

The first uses 'super' to add the action to itself.  The second adds the action 
to its 'container'.

That difference allows you to add a mutually_exclusive_group to an 
argument_group (or to another mutually_exclusive_group), but you can't add an 
argument_group to another argument_group (no nesting).

I don't like the idea of using a different _add_action method depending on 
whether group has a 'title' or not.  That's too kludgy.

Another possibility is to have 'parser.add_mutually_exclusive_group()' do what 
I first demonstrated - first create an 'argument_group' with the title, and add 
the mutually_exclusive_group to that.  This is still kludgy, but the change is 
limited to one function.  For demonstration purposes it probably could be 
implemented in a new function (add_titled_mutually_exclusive_group).

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[paul j3]

paul j3 added the comment:

While mutually exclusive groups are a subclass of argument groups, they have 
very different uses.

Argument groups are used solely to organize the help section. Groups are not 
used at all during parsing.  'parse_args' doesn't even pay attention to those 2 
default groups (positionals and optionals).  'parse_args' just uses the master 
list of actions ('parser._actions'). 

Mutually exclusive groups are not used at all while formatting the help lines.  
They are used to format the usage line.  They also implement argument tests 
during parsing.

Groups are not set up for nesting.  However it is possible to define a mutually 
exclusive group within an argument group, and effectively give it a title and 
description.

p=argparse.ArgumentParser()
g=p.add_argument_group('title')
g1=g.add_mutually_exclusive_group()
g1.add_argument('--foo')
p.print_help()

producing:

usage: ipython [-h] [--foo FOO]
optional arguments:
  -h, --help  show this help message and exit
title:
  --foo FOO

Both kinds of groups are a superficial addition to argparse.  I argue in 
http://bugs.python.org/issue11588 that they aren't adequate for handling more 
complicated groupings (inclusive, nesting, etc).

While I'm not convinced the change proposed in this issue is necessary, if we 
are going implement it, I'd suggest a simple addition to 
'add_mutually_exclusive_group()'.  If there's a title argument, add this group 
to '_action_groups' as well as '_mutually_exclusive_groups'.

def add_mutually_exclusive_group(self, **kwargs):
group = _MutuallyExclusiveGroup(self, **kwargs)
self._mutually_exclusive_groups.append(group)
try:
kwargs.title
self._action_groups.append(group)
except AttributeError:
pass
return group

This should do the job without adding much complexity.

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[Tatiana Al-Chueyr]

Tatiana Al-Chueyr added the comment:

uploading test file

--
Added file: http://bugs.python.org/file34845/test_argparse_mutex_with_title.py

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[Tatiana Al-Chueyr]

Changes by Tatiana Al-Chueyr :


Removed file: http://bugs.python.org/file34844/test_argparse_mutex_with_title.py

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[Tatiana Al-Chueyr]

Tatiana Al-Chueyr added the comment:

My proposal is that both:
- add_mutually_exclusive_group()
- add_argument_group()

print optional arguments in the same way when title and/or description are 
provided.

I've attached a test case of the proposed behavior.

Please, let me know if you have any objections or suggestions! :)

I'm working on the implementation right now.

Note: it is outside the existing Lib/test/test_argparse.py for clarifying the 
idea.

BTW: thanks to r.david.murray for mentoring and discussing use cases!

--
nosy: +paul.j3, r.david.murray, tati_alchueyr
Added file: http://bugs.python.org/file34844/test_argparse_mutex_with_title.py

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[Tshepang Lekhonkhobe]

Changes by Tshepang Lekhonkhobe :


--
nosy: +tshepang

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[issue17218] support title and description in argparse add_mutually_exclusive_group

[Chris Jerdonek]

New submission from Chris Jerdonek:

This issue is to add to argparse's add_mutually_exclusive_group() method 
support for passing a title and description.  From the argparse docs:

"Note that currently mutually exclusive argument groups do not support the 
title and description arguments of add_argument_group()."

(from 
http://docs.python.org/dev/library/argparse.html#argparse.add_mutually_exclusive_group
 )

--
components: Library (Lib)
messages: 182251
nosy: bethard, chris.jerdonek
priority: normal
severity: normal
stage: test needed
status: open
title: support title and description in argparse add_mutually_exclusive_group
type: enhancement
versions: Python 3.4

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