Using Argparse and Json together

The args Namespace from parse_args can be transformed into a dictionary with:

argparse_dict = vars(args)

The JSON values are also in a dictionary, say json_dict. You can copy selected values from one dictionary to the other, or do a whole scale update:

argparse_dict.update(json_dict)

This way the json_dict values over write the argparse ones.

If you want to preserve both, you either need to have different argument (key) names, or the values have to be lists, which you can append or extend. That takes a bit more work, starting with using the correct nargs value in argparse.

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The revised parser produces, with a test input:

In [292]: args=parser.parse_args('-p one -q two -r three'.split())
In [293]: args
Out[293]: Namespace(param1='one', param2='two', param3='three')
In [295]: args_dict = vars(args)    
In [296]: args_dict
Out[296]: {'param1': 'one', 'param2': 'two', 'param3': 'three'}

The JSON string, when parsed (json.loads?) produces a dictionary like:

In [317]: json_dict
Out[317]: 
{'testOwner': 'my name',
 'testParameters': {'test1': {'param1': '0', 'param2': '20', 'param3': 'True'},
  'test2': {'param1': 'cc'}},
 'tests': ['test1', 'test2', 'test3']}

I produced this by pasting your display into my Ipython session, but I think the JSON loader produces the same thing

The argparse values could be added with:

In [318]: json_dict['testParameters']['test3']=args_dict
In [319]: json_dict
Out[319]: 
{'testOwner': 'my name',
 'testParameters': {'test1': {'param1': '0', 'param2': '20', 'param3': 'True'},
  'test2': {'param1': 'cc'},
  'test3': {'param1': 'one', 'param2': 'two', 'param3': 'three'}},
 'tests': ['test1', 'test2', 'test3']}

Here I added it as a 3rd test set, taking (by conincidence) a name from the tests list. json_dict['testParameters']['test2']=args_dict would replace the values of test2.

One way to add the args values to the undefined values of 'test2' is:

In [320]: args_dict1=args_dict.copy()    
In [322]: args_dict1.update(json_dict['testParameters']['test2'])
In [324]: json_dict['testParameters']['test2']=args_dict1
In [325]: json_dict
Out[325]: 
{'testOwner': 'my name',
 'testParameters': {'test1': {'param1': '0', 'param2': '20', 'param3': 'True'},
  'test2': {'param1': 'cc', 'param2': 'two', 'param3': 'three'},
  'test3': {'param1': 'one', 'param2': 'two', 'param3': 'three'}},
 'tests': ['test1', 'test2', 'test3']}

I used this version of update to give priority to the 'cc' value in the JSON dictionary.

Turns out to be pretty easy with the following caveats

1. The setup overrides values in config files with values on the command line
2. It only uses default values if options have not been set on the command line nor the settings file
3. It does not check that the settings in the config file are valid

import argparse
import json

parser = argparse.ArgumentParser()

parser.add_argument('--save_json',
    help='Save settings to file in json format. Ignored in json file')
parser.add_argument('--load_json',
    help='Load settings from file in json format. Command line options override values in file.')

args = parser.parse_args()

if args.load_json:
    with open(args.load_json, 'rt') as f:
        t_args = argparse.Namespace()
        t_args.__dict__.update(json.load(f))
        args = parser.parse_args(namespace=t_args)

# Optional: support for saving settings into a json file
if args.save_json:
    with open(args.save_json, 'wt') as f:
        json.dump(vars(args), f, indent=4)