Python: argparse optional arguments without dashes

Question

I would like to have the following syntax:

python utility.py file1 FILE1 file2 FILE2

where file1 and file2 are optional arguments. It is simple to make it working with this syntax:

python utility.py --file1 FILE1 --file2 FILE2

using

parser.add_argument('--file1',type=file)
parser.add_argument('--file2',type=file)

however, if I remove the dashes, argparse starts to interprete it as a positional rather than optional argument...

In other words, is it possible to specifically tell argparse whether an argument is optional or positional so that I can have optional parameters without the dashes?

That syntax (no dashes) is confusing as hell! There is a reason the convention exists. — Martijn Pieters, Jul 03 '12 at 12:15
@MartijnPieters: it may be confusing but for some scientific applications this is a standard... [example](http://www.ccp4.ac.uk/html/refmac5/description.html) — jvm, Jul 03 '12 at 12:19
@MartijnPieters: counterexample: the `git` or `svn` command line interface. — Rody Oldenhuis, Jul 14 '14 at 14:21
@RodyOldenhuis: those are subcommands, not switches. Each subcommand takes options, which use dashes. — Martijn Pieters, Jul 14 '14 at 14:34
@MartijnPieters: that is just semantics, no difference from the syntax point of view - arguments with no dashes. Not (directly) supported by argparse for whatever semantics. BTW, they are not switches in my example either (but that is irrelevant as I have just mentioned). — jvm, Dec 30 '14 at 17:56
@jvm: subcommands do not usually share switches. There is a shared level (`git --version`) and per-subcommand switches (`git checkout --patch`). Don't just dismiss the semantics here. — Martijn Pieters, Dec 30 '14 at 19:31

mgilson · Accepted Answer · 2012-07-03T16:21:34.113

13

There is no way to get argparse to do this for you. However, you can make argparse accept any number of positional arguments:

parser.add_argument('FILES',nargs='*')
options=parser.parse_args()
file1,optional_files=options.FILES[0],options.FILES[1:]

Of course, you may want to add some checks to make sure that at least 1 file was given, etc.

EDIT

I'm still not 100% sure what you want here, but if file1 and file2 are literal strings, you can work around that a little bit by preprocessing sys.argv. Of course, this will still format your help message strangely, but you can always add an epilog explaining that either form is OK:

import argparse
import sys

mangle_args=('file1','file2')
arguments=['--'+arg if arg in mangle_args else arg for arg in sys.argv[1:]]

parser=argparse.ArgumentParser()
parser.add_argument('--file1')
parser.add_argument('--file2')
options=parser.parse_args(arguments)

edited Jul 03 '12 at 16:21

answered Jul 03 '12 at 12:15

mgilson

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Positional arguments are not sufficient for me. For example, file1 may be skipped, file2 inputted, file3 skipped, file4 inputted and the assignment is important (ie I need to know that it was file2 and file4 that were specified by the user) – jvm Jul 03 '12 at 12:33
1

@jvm -- How is argparse (or anything) supposed to know that the file you gave is `file2` instead of `file1`? If you can't sort it out from the order it came on the commandline, certainly `argparse` can't do it either. – mgilson Jul 03 '12 at 12:43
Are `file1` and `file2` constant strings, or are they names of files -- maybe that's what I'm not understanding here... – mgilson Jul 03 '12 at 12:45
@jvm -- I think I now understand what you're trying to do. I've posted a "workaround". It's a little ugly, but it might be good enough for your purposes. – mgilson Jul 03 '12 at 13:25
1

Thanks, this is a working solution indeed. I was hoping I was missing some argparse function that would allow me this directly but if that is not possible then your workaround is probably the best. Just some nitpicking - of course you also need to import argparse in your example. – jvm Jul 03 '12 at 16:16
@jvm -- I left it off because you did in your original example. Anyway, it's in there now. – mgilson Jul 03 '12 at 16:22
@mgilson, it's a good workaround but `--help` still contains those dashes. – Kiran Kumar Kotari Jul 18 '22 at 08:34

score 3 · Answer 2 · answered Jul 30 '18 at 11:28

Another Example would be:

train.py

import argparse
if __name__ == '__main__':
    parser = argparse.ArgumentParser(description="Arguments for wake_word")
    parser.add_argument('data', type=str, help="path to data")
    parser.add_argument('output', type=str, help="model save path")
    parser.add_argument('batch_size', type=int, help="batch size")
    parser.add_argument('epochs', type=int, help="no.s of epochs")
    args = parser.parse_args()
print(args.data + args.output + args.batch_size + args.epochs)

then you can just run this code with arguments without dash

train.py /path/to/data/ /path/to/output_files/ 128 100

And, in ascending order

the question is talking about optional arguments without dashes, not positional arguments — Kiran Kumar Kotari, Jul 18 '22 at 08:28

mc.dev · Answer 3 · 2019-05-03T00:42:19.520

1

Had same problem. My workaround is:

lastarg = sys.argv[-1]
if len(sys.argv) > 1 and lastarg[0] != '-':
    sys.argv[-1] = '-file'
    sys.argv.append(lastarg)

argparser = argparse.ArgumentParser()
argparser.add_argument('-d', action='store_true')
argparser.add_argument('-nrv', action='store_true')
argparser.add_argument('-file', type=str, default='')
args = argparser.parse_args()

edited May 03 '19 at 00:42

answered May 03 '19 at 00:29

mc.dev

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Python: argparse optional arguments without dashes

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