[issue29553] Argparser does not display closing parentheses in nested mutex groups

[Christoph Stahl]

New submission from Christoph Stahl:

When creating nested mutually exclusive groups, all closing brackets except one 
are omitted.

Example:
parser = ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument('-a')
group.add_argument('-b')
group2 = group.add_mutually_exclusive_group()
group2.add_argument('-c')
group2.add_argument('-d')
group3 = group2.add_mutually_exclusive_group()
group3.add_argument('-e')
group3.add_argument('-f')

prints a usage line of:
usage: test.py [-h] [-a A | -b B | [-c C | -d D | [-e E | -f F]

it should print something like:
usage: test.py [-h] [-a A | -b B | [-c C | -d D | [-e E | -f F]]]

--
components: Library (Lib)
messages: 287776
nosy: christofsteel
priority: normal
severity: normal
status: open
title: Argparser does not display closing parentheses in nested mutex groups
versions: Python 2.7, Python 3.6

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[issue29553] Argparser does not display closing parentheses in nested mutex groups

[Christoph Stahl]

Changes by Christoph Stahl :


--
type:  -> behavior

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[issue29553] Argparser does not display closing parentheses in nested mutex groups

[Christoph Stahl]

Christoph Stahl added the comment:

Hi,

I thought a bit about the problem and came up with the following:

The | in the usage is de facto an XOR operator. Exactly one of the options can 
be used. The XOR operator has the associative property, meaning:

  (A XOR B) XOR C = A XOR (B XOR C)

So translated to the | this means:
  
  [[ -a | -b ] | -c ] = [ -a | [ -b | -c ]]

usually one writes:

  [ -a | -b | -c ]

So I propose dropping the inner brackets altogether.

--

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