Parses `xxx:yyy` or a stringified JSON map as a dictionary (for use with CLI `ArgumentParser`)

key_value_string_parser.py

# Copyright (c) 2018 Genome Research Limited
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import json
from argparse import Action
from json import JSONDecodeError


class KeyValueStringParserAction(Action):
    """
    Parses input in the form `xxx:yyy` or a stringified JSON map as a key value pair.

    Accepts multiple key-value pairs in stringified JSON map.

    e.g.
    ```
    parser.add_argument(f"-{MY_SHORT_PARAMETER}", f"--{MY_LONG_PARAMETER}", action=StringDictParseAction)
    ```
    """
    def __call__(self, parser, namespace, values, option_string=None):
        try:
            value_as_json = json.loads(values)
            if type(value_as_json) is not dict:
                raise ValueError(f"Not an acceptable JSON value: {values}")
            getattr(namespace, self.dest, {}).update(value_as_json)
        except JSONDecodeError:
            if ":" not in values:
                raise ValueError(f"Unable to parse: {values}. Must be in form \"xxx:yyy\"")
            key, value = values.split(":")
            getattr(namespace, self.dest, {})[key] = value