argparse module How to add option without any argument?

Question

I have created a script using argparse.

The script needs to take a configuration file name as an option, and user can specify whether they need to proceed totally the script or only simulate it.

The args to be passed: ./script -f config_file -s or ./script -f config_file.

It's ok for the -f config_file part, but It keeps asking me for arguments for the -s which is optionnal and should not be followed by any.

I have tried this:

parser = argparse.ArgumentParser()
parser.add_argument('-f', '--file')
#parser.add_argument('-s', '--simulate', nargs = '0')
args = parser.parse_args()
if args.file:
    config_file = args.file
if args.set_in_prod:
        simulate = True
else:
    pass

With the following errors:

File "/usr/local/lib/python2.6/dist-packages/argparse.py", line 2169, in _get_nargs_pattern
nargs_pattern = '(-*%s-*)' % '-*'.join('A' * nargs)
TypeError: can't multiply sequence by non-int of type 'str'

And same errror with '' instead of 0.

Answer 1

As @Felix Kling suggested, to create an option that needs no value, use action='store_true', 'store_false' or 'store_const'. See documentation.

>>> from argparse import ArgumentParser
>>> p = ArgumentParser()
>>> _ = p.add_argument('-f', '--foo', action='store_true')
>>> args = p.parse_args()
>>> args.foo
False
>>> args = p.parse_args(['-f'])
>>> args.foo
True