Serializable

output.txt

{
  "b": {
    "param": "yello!"
  },
  "a": "test"
}

serializable.py

import json


class Serializable(object):
    class _CustomEncoder(json.JSONEncoder):
        def default(self, obj):
            return obj.__dict__ if isinstance(obj, Serializable) else obj

    def __repr__(self):
        return json.dumps(self, indent=2, cls=Serializable._CustomEncoder)


class A(Serializable):
    def __init__(self, a):
        self.a = a
        self.b = B("yello!")


class B(Serializable):
    def __init__(self, param):
        self.param = param


print(A("test"))