Python: Dump & Load partially known / dynamic JSON. Using dataclasses (type safe).

json.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

# Requirements:
# Python 3.7+
# pip install dataclasses-json


import dataclasses as dc
import os
import sys
import traceback
from typing import List

import dataclasses_json as dcjson


@dcjson.dataclass_json(letter_case=dcjson.LetterCase.CAMEL, undefined=dcjson.Undefined.INCLUDE)
@dc.dataclass()
class Nested:
    nested_known_key: int = dc.field(metadata=dcjson.config(field_name='nestedKnownKey'))
    # Unknown fields go here:
    unknown: dcjson.CatchAll
    # Field sample for internal needs, excluded from JSON processing:
    excluded: int = dc.field(default=0, metadata=dcjson.config(exclude=dcjson.cfg.Exclude.ALWAYS))


@dcjson.dataclass_json(letter_case=dcjson.LetterCase.CAMEL, undefined=dcjson.Undefined.INCLUDE)
@dc.dataclass()
class Top:
    top_known_key: int = dc.field(metadata=dcjson.config(field_name='topKnownKey'))
    nested_known_array: List[Nested] = dc.field(metadata=dcjson.config(field_name='nestedKnownArray'))
    # Unknown fields go here:
    unknown: dcjson.CatchAll
    # Field sample for internal needs, excluded from JSON processing:
    excluded: int = dc.field(default=0, metadata=dcjson.config(exclude=dcjson.cfg.Exclude.ALWAYS))


class App:

    @staticmethod
    def main() -> None:
        json_str: str = """
        {
            "topKnownKey": 1,
            "topUnknownKey": 2,
            "nestedKnownArray": [
                {
                    "nestedKnownKey": 3,
                    "nestedUnknownKey": 4
                },
                {
                    "nestedKnownKey": 5,
                    "nestedUnknownKey": 6
                }
            ],
            "nestedUnknownArray": [
                {
                    "nestedKnownKey": 7,
                    "nestedUnknownKey": 8
                }
            ]
        }
        """

        # Decode.
        # noinspection Mypy
        top: Top = Top.from_json(json_str)

        # Modify.
        top.top_known_key = 100
        top.excluded = 200
        top.nested_known_array[0].nested_known_key = 300
        top.nested_known_array[0].excluded = 400

        # Encode.
        # noinspection Mypy
        out: str = top.to_json(indent=2)

        # Print output.
        print(out)
        input('Press <Enter> to exit...\n')


# Main start point.
if __name__ == '__main__':
    # noinspection PyBroadException
    try:
        os.chdir(sys.path[0])

        App.main()
    except Exception:
        traceback.print_exc()

        input('Press <Enter> to exit...\n')

        exit(1)