json decimal and datetime

import json
import datetime


class SupplementaryEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, decimal.Decimal):  # for decimal
            return float(obj)
        elif isinstance(obj, datetime.datetime):  # for datetime
            return obj.strftime("%Y-%m-%d %H:%M:%S")
        return json.JSONEncoder.default(self, obj)

test_dict = {"a": datetime.datetime.now()}
res = json.dumps(test_dict, cls=SupplementaryEncoder)