How do I get back the option string using argparse?

Question

parser = argparse.ArgumentParser()
parser.add_argument("-p", "--pattern", help="Pattern file")
args = parser.parse_args()

Now is it possible to get back the string "--pattern" from args? I need the string so that I can construct a cmd list to pass to Popen like Popen(['some_other_program', args.pattern.option_string, args.pattern], ...) without repeating it (and having to maintain it in two places) (Popen(['some_other_prog', '--pattern', args.pattern], ...)).

I need to create a wrapper for another program. Some of the args need to be passed to the wrapped program (via Popen) and some are required by the wrapper.

---

Is there a better method than the following example?

pass_1 = '--to-be-passed'
parser = argparse.ArgumentParser()
parser.add_argument("-p", pass_1, help="Pass me on")
parser.add_argument("-k", "--arg-for-wrapper")
args = parser.parse_args()

...
process = Popen(['wrapped_program', pass_1, args.pass_1], ...)
... 

This method of keeping the args in variables is not very good as:

1. Maintaining short options along with long options becomes difficult.
2. Popen if called in another function requires passing these variables(or a dict of them) to the function. This seems redundant as args passed to it should be sufficient.

Answer 1

Add a dest to your add_argument call.

parser.add_argmument("p", "--pattern", dest="pattern", help="your help text")
args = parser.parse_args()
args = vars(args)

The you can reference the pattern with args["pattern"] .

Answer 2

There doesn't seem to be an easy way to get the original option strings from the result of a parser.parse_args(), but you can get them from the parser object. You just need to peek into its __dict__, in order to retrieve the parser settings after it's created. In your case you want the _option_string_actions field. Unfortunately this doesn't seem officially supported, as I couldn't find a ArgumentParser method dedicated to this, so YMMV. On Python 3:

Demo:

parser = argparse.ArgumentParser()
parser.add_argument('--foo', '-f', type=int, default=1000, help='intensity of bar')
parser.add_argument('--bar', '-b', type=str, default='bla', help='whatever')
store_action_dict=vars(parser)['_option_string_actions']
print(store_action_dict.keys())    # dict_keys(['--help', '-b', '-f', '-h', '--foo', '--bar'])