Python JSON Decoder

json_decoder.py

import json

from decimal import Decimal


class A:
    def __init__(self, value):
        self.bar = Decimal(value)
    def to_dict(self):
        return {
            "bar": self.bar
        }

class Encoder(json.JSONEncoder):
    def default(self, o):
        if isinstance(o, A):
            return o.to_dict()
        if isinstance(o, Decimal):
            return float(o)
        return json.JSONEncoder.default(self, o)

a = A(2)
json.dumps(a, cls=Encoder)