Change parameter display name (two names) with argparse in Python

Question

I'm writing a program that uses argparse, for parsing some arguments that I need. For now I have this:

parser.add_argument('--rename', type=str, nargs=2, help='some help')

When I run this script I see this:

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

How can I change my code so that the help will show this?

--rename OLDFILE NEWFILE

Can I then use OLDFILE and NEWFILE value in this way?

args.rename.oldfile
args.rename.newfile

wjandrea · Accepted Answer · 2025-10-12 17:34:08Z

57

If you set metavar=('OLDFILE', 'NEWFILE'):

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('--rename', type=str, nargs=2, help='some help',
                    metavar=('OLDFILE', 'NEWFILE'))
args = parser.parse_args()
print(args)

Then test.py -h yields

usage: test.py [-h] [--rename OLDFILE NEWFILE]

optional arguments:
  -h, --help            show this help message and exit
  --rename OLDFILE NEWFILE
                        some help

You can then access the arguments with

oldfile, newfile = args.rename

If you really want to access the oldfile with args.rename.oldfile you could set up a custom action:

import argparse
class RenameAction(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        setattr(namespace, self.dest,
                argparse.Namespace(
                    **dict(zip(('oldfile', 'newfile'),
                               values))))

parser = argparse.ArgumentParser()
parser.add_argument('--rename', type=str, nargs=2, help='some help',
                    metavar=('OLDFILE', 'NEWFILE'),
                    action=RenameAction)
args = parser.parse_args()

print(args.rename.oldfile)

but it extra code does not really seem worth it to me.

edited Oct 12 at 17:34

wjandrea

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answered Aug 22, 2013 at 9:54

unutbu

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1 Comment

Wolfy Over a year ago

thanks for all details provided... "oldfile, newfile = args.rename" will do the job :)

njzk2 · Accepted Answer · 2013-08-22 09:58:16Z

1

Read the argparse documentation (http://docs.python.org/2.7/library/argparse.html#metavar):

Different values of nargs may cause the metavar to be used multiple times. Providing a tuple to metavar specifies a different display for each of the arguments:

>>> parser = argparse.ArgumentParser(prog='PROG')
>>> parser.add_argument('-x', nargs=2)
>>> parser.add_argument('--foo', nargs=2, metavar=('bar', 'baz'))
>>> parser.print_help()
usage: PROG [-h] [-x X X] [--foo bar baz]

optional arguments:
 -h, --help     show this help message and exit
 -x X X
 --foo bar baz

answered Aug 22, 2013 at 9:58

njzk2

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