[issue14454] argparse metavar list parameter with nargs=k

[Andy Harrington]

New submission from Andy Harrington <aharrin at luc.edu>:

I now set the help string for an
argparse option with two parameters: 

parser.add_argument('-s', '--substitute', nargs=2,
                    help='Replace first string with second',
                    metavar='string')

which generates a help message

  -s string string, --substitute string string
                    Replace first string with second

Instead I would *like* to generate the help message

  -s fromString toString, --substitute fromString toString
                    Replace fromString with toString
                    
At present metavar replaces each of multiple parameters with the same thing,
but with a fixed number of parameters it makes sense that each may have a
different meaning.

It seems to me that when nargs=k is set for an integer k,
we could have metavar be a list of k strings to go in the k places,
as in

parser.add_argument('-s', '--substitute', nargs=2,
                    help='Replace fromString with toString',
                    metavar=['fromString', 'toString'])

and have this generate my desired help message.

There is no need to break the current behavior:
The parser can distinguish a list from a single string. 

The same text is in the attached file.

----------
components: Library (Lib)
files: metavarListEnhancement.txt
messages: 157148
nosy: andyharrington
priority: normal
severity: normal
status: open
title: argparse metavar list parameter with nargs=k
type: enhancement
versions: Python 3.3
Added file: http://bugs.python.org/file25074/metavarListEnhancement.txt

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