json_dataclasses.py

from typing import List, Dict, Type
from dataclasses import dataclass


# importing separately to make clear which names come from dataclasses
import dataclasses
from pprint import pprint
import json




JSON_TYPES = [str, int, dict, float, bool, tuple, list, type(None)]


def deserialize_dataclasses(dct):
    if "__dataclass__" in dct:
        dataclass_ = DataclassFriendlyJsonEncoder.__dataclassses__[dct["__dataclass__"]]
        del dct["__dataclass__"]
        return dataclass_(
            **{
                k: v if not isinstance(v, dict) else deserialize_dataclasses(v)
                for k, v in dct.items()
            }
        )
    return dct


class DataclassFriendlyJsonEncoder(json.JSONEncoder):
    __dataclassses__: Dict[str, Type] = {}
    def default(self, obj):
        if dataclasses.is_dataclass(obj):
            return {
                **dict(__dataclass__=obj.__class__.__name__),
                **{
                    field.name: self.default(getattr(obj, field.name))
                    for field in dataclasses.fields(obj)
                },
            }
        elif type(obj) in JSON_TYPES:
            return obj
        super(DataclassFriendlyJsonEncoder, self).default(obj)


def register_dataclass(cls):
    DataclassFriendlyJsonEncoder.__dataclassses__[cls.__name__] = cls
    return cls

@register_dataclass
@dataclass
class Bar:
    a: str
    b: str

@register_dataclass
@dataclass
class Foo:
    a: str
    b: List[int]
    bar: Bar


foo = Foo("a", [1, 2], Bar("a", "b"))
foojson = json.dumps(foo, cls=DataclassFriendlyJsonEncoder)
pprint(json.loads(foojson, object_hook=deserialize_dataclasses))