28
import argparse

class customAction(argparse.Action):
    def __call__(self, parser, args, values, option_string=None):
       setattr(args, self.dest, values)

parser = argparse.ArgumentParser()
parser.add_argument('-e', '--example', action=customAction)

I want to pass additional arguments to customAction when the option -e is triggered, e.g. a instance of another class. How can I do this? Everything I have tried has errored out.

2 Answers2

49
def make_action(additional_arg):
    class customAction(argparse.Action):
        def __call__(self, parser, args, values, option_string=None):
            print(additional_arg)
            setattr(args, self.dest, values)
    return customAction
#...
parser.add_argument('-e', '--example', action=make_action('your arg'))
Neil
  • 24,551
  • 15
  • 60
  • 81
jfs
  • 399,953
  • 195
  • 994
  • 1,670
21

Another solution is to derive the based class argparse.Action like this:

class CustomAction(argparse.Action):
    def __init__(self,option_strings,
                 additional_arg1,additional_arg2,
                 dest=None,
                 nargs=0,
                 default=None,
                 required=False,
                 type=None,
                 metavar=None,
                 help=None):
        self._a1=additional_arg1
        self._a2=additional_arg2
        super(CustomAction, self).__init__(
            option_strings=option_strings,
            dest=dest,
            nargs=nargs,
            default=default,
            required=required,
            metavar=metavar,
            type=type,
            help=help)
    def __call__(self, parser, namespace, values, option_string=None):
        print(self._a1)
        print(self._a2)
        setattr(namespace, self.dest, values)

#........
parser.add_argument('-e', '--example', action=CustomAction, additional_arg1='your arg', additional_arg2=42)

Alternatively, supply *args and **kwargs to pass through any additional parameters to the parent constructor.

class CustomAction(argparse.Action):
    def __init__(self, option_strings, additional_arg1, additional_arg2,
                 *args, **kwargs):
        self._a1 = additional_arg1
        self._a2 = additional_arg2
        super(CustomAction, self).__init__(option_strings=option_strings,
                                           *args, **kwargs)
    def __call__(self, parser, namespace, values, option_string=None):
        print(self._a1)
        print(self._a2)
        setattr(namespace, self.dest, values)

#........
parser.add_argument('-e', '--example', action=CustomAction, additional_arg1='your arg', additional_arg2=42)
FeRD
  • 1,699
  • 15
  • 24
BiBi
  • 211
  • 2
  • 2
  • As much as I love closures, this answer strikes me as a cleaner (if more object-oriented) solution. Anyone using this might consider adding `*args` and `**kwargs` instead of listing out all of argparse's default `Action` arguments. – Alexander Bauer Jul 21 '15 at 11:04
  • 4
    this example I needed to change setattr(args to setattr(namespace to make it work – kdubs Mar 29 '17 at 21:54
  • @kdubs I've made an edit to the answer, correcting that issue. – FeRD Sep 03 '23 at 05:20