python3 argparse example with importable default settings

args_example.py

#!/usr/bin/python3
'''
> python3 args_example.py -h
usage: args_example.py [-h] [-f FIRST_OPTION] [-s SECOND_OPTION]
                       [-t THIRD_OPTION]
                       mandatory_argument

Example argument parser with default values.

positional arguments:
  mandatory_argument    Not everything can have a default value. This is a
                        mandatory argument.

optional arguments:
  -h, --help            show this help message and exit
  -f FIRST_OPTION, --first_option FIRST_OPTION
                        This is the first option. Default:
                        first_default_value.
  -s SECOND_OPTION, --second_option SECOND_OPTION
                        This is the second option. (Default:
                        second_default_value)
  -t THIRD_OPTION, --third_option THIRD_OPTION
                        This is the third option. (Default:
                        third_default_value)

> python3 args_example.py -f "non-default first value" --second_option 'non-default second value' "this is mandatory"
{'first_option': 'non-default first value',
 'mandatory_argument': 'this is mandatory',
 'second_option': 'non-default second value',
 'third_option': 'third_default_value'}

Of course, https://pymotw.com/2/argparse/ is still excellent.
'''


import argparse
import pprint


default_settings = {'first_option': 'first_default_value',
                    'second_option': 'second_default_value',
                    'third_option': 'third_default_value'}


def get_args(settings=default_settings):
    '''Reads from sys.stdin. Use stdin to get new options, and return options 
    merged with the default options. Settings is a dictionary. We'll have an
    argument (no, you came here for an argument), set two options, and default 
    one.
    '''

    parser = argparse.ArgumentParser(description='Example argument parser with default values.')
    parser.add_argument('mandatory_argument', help='Not everything can have a default value. This is a mandatory argument.')
    parser.add_argument('-f', '--first_option', help='This is the first option. Default: %(default)s.',
                        default=settings['first_option'])
    parser.add_argument('-s', '--second_option', help='This is the second option. (Default: %(default)s)',
                        default=settings['second_option'])
    parser.add_argument('-t', '--third_option', help='This is the third option. (Default: %(default)s)',
                        default=settings['third_option'])
    args = parser.parse_args()
    args_settings = vars(args) # everything is easier with a dictionary
    
    #python3.5+
    merged_settings_3 = {**settings, **args_settings}

    #python2
    merged_settings_2 = default_settings.copy()
    merged_settings_2.update(args_settings)

    merged_settings_brute_force = '''
    if args.first_option:
        settings['first_option'] = args.first_option
    if args.second_option:
        settings['second_option'] = args.second_option
    if args.third_option:
        settings['third_option'] = args.third_option
    settings['mandatory_argument'] = args.mandatory_argument 
    return merged_settings_brute_force
        '''

    return merged_settings_3


def main():
    settings = get_args()
    pprint.pprint(settings)


if __name__ == '__main__':
    main()