python - How to parse positional arguments with leading minus sign (negative numbers) using argparse

Question

I would like to parse a required, positional argument containing a comma-separated list of integers. If the first integer contains a leading minus ('-') sign, argparse complains:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('positional')
parser.add_argument('-t', '--test', action='store_true')
opts = parser.parse_args()
print opts

$ python example.py --test 1,2,3,4
Namespace(positional='1,2,3,4', test=True)

$ python example.py --test -1,2,3,4
usage: example.py [-h] [-t] positional
example.py: error: too few arguments

$ python example.py --test "-1,2,3,4"
usage: example.py [-h] [-t] positional
example.py: error: too few arguments

I've seen people suggest using some other character besides - as the flag character, but I'd rather not do that. Is there another way to configure argparse to allow both --test and -1,2,3,4 as valid arguments?

Answer 1

You need to insert a -- into your command-line arguments:

$ python example.py --test -- -1,2,3,4
Namespace(positional='-1,2,3,4', test=True)

The double-dash stops argparse looking for any more optional switches; it's the defacto standard way of handling exactly this use case for command-line tools.