Python argparse with either a template or options

template_parser.py

#! /usr/bin/env python

"""
If template file "template.conf" contains:
   ["--foo", "sausage", "--bar", "egg"]
Calling:
    $ python ./parser.py template template.conf
Will be equivalent to calling:
    $ python ./parser.py options --foo sausage --bar egg
And the initial option we attach to the parser needs to appear before the command:
    $ python -v ./parser.py template template.conf
"""

import argparse
import json

def arguments_from_template(arguments, parser):
    if 'template_fn' in arguments:
        if arguments.verbose:
            print('Arguments with template action:')
            print(json.dumps(vars(arguments)))
        ind_args = []
        with open(arguments.template_fn) as f:
            template_dict = json.load(f)
            for key, value in template_dict.items():
                if value:
                    ind_args.extend(['--' + key, str(value)])
                else:
                    ind_args.extend(['--' + key])
            ind_args.insert(0, "options")
            orig_args = arguments
            arguments = parser.parse_args(ind_args)
            arguments.__dict__.update(vars(orig_args))
    if arguments.verbose:
        print('Arguments with options action:')
        print(json.dumps(vars(arguments)))
    return arguments

if __name__ == '__main__':
   
    parser = argparse.ArgumentParser(description='Template parser example')

    # Add an argument that works for all parsers
    parser.add_argument('-v', '--verbose', action='store_true',
                        help='Do we print the results we obtain after running the commands?')
    subparsers = parser.add_subparsers(help='commands')

    # Add a subparser for the template action
    subparse_template = subparsers.add_parser('template', help='Use a template')
    subparse_template.add_argument('template_fn', help='Template to use')

    # Add a subparser for the individual option action
    subparse_args = subparsers.add_parser('options', help='Use arguments')
    subparse_args.add_argument('-f', '--foo', required=True, type=str,
                               help='Foo value')
    subparse_args.add_argument('-b', '--bar', required=True, type=str,
                               help='Bar value')

    arguments = parser.parse_args()
    # If we are using the template command...

    arguments = arguments_from_template(arguments, parser)