How to convert Class Object to JSON in Python

Question

import json

class Abc:

    firstName = ''
    secondName = ''

obj = Abc()

obj.firstName = 'Raj'

res = json.dumps(obj, default=lambda o: o.__dict__)

print(res)

Output: {"firstName": "Raj"}

But I need the Output like this

{"firstName": "Raj", "secondName": ""}

Any Solution for this??

Try giving the class a constructor and create as member fields. Ex: this.firstName = '' and this.secondName = '' — 001
– 001, Commented May 20, 2021 at 13:55
Does this answer your question? How to make a class JSON serializable — C.Nivs
– C.Nivs, Commented May 20, 2021 at 13:58
For simple classes only containing data and no interface, you might be interested in checking the dataclasses. — joubs
– joubs, Commented May 20, 2021 at 13:59

chepner · Accepted Answer · 2021-05-20 13:57:25Z

1

First, start with a proper class definition.

class Abc:
    def __init__(self, first='', second=''):
        self.firstName = first
        self.secondName = second

Then define an appropriate JSONEncoder subclass:

import json


class AbcEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Abc):
            return {"firstName": obj.firstName, "secondName": obj.secondName}
        return super().default(obj)


obj = Abc("Raj")
res = json.dumps(obj, cls=AbcEncoder)

answered May 20, 2021 at 13:57

chepner

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7 Comments

C.Nivs Over a year ago

Not your downvoter, but if I were to, it would be because there's a duplicate for this question and answer already

Lokesh Jinka Over a year ago

I cannot use this AbcEncoder method because in my program class contains 30 variables........ I gave simple question to understand the problem

chepner Over a year ago

I don't see how the number of variables is relevant.

chepner Over a year ago

@Civs Fair enough, though I think the class definition needed pointing out. (For example, one of the answers in the dupe suggests passing the instance's __dict__ attribute to json.dumps, but that won't apply since secondName in the original code is a class attribute and won't be in obj.__dict__.)

chepner Over a year ago

(I kind of wish json supported __to_json__ and __from_json__ hooks that you could add to your classes, but I haven't really thought out what problems that might introduce.)

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