python 2.7 : TypeError: <main.nested_object object at 0x...> is not JSON serializable

Question

I'm trying to run the json.dumps method on a nested class/object and it fails on TypeError: <__main__.nested_object object at 0x...> is not JSON serializable

What should I change in my class so I could call json.dumps method with input parameters of an implementation of JSONEncoder?

Here is a very simple code that simulate the problem:

class leaf_object(object):
    def __init__(self, s):
        self.value = s

class nested_object(object):
    def __init__(self, a, b_list):
        self.a = a
        self.b_list = b_list

if __name__ == "__main__":
    obj = nested_object('a1', [leaf_object('a1.1'),leaf_object('a1.2')])
    import json
    print(json.dumps(obj))

It doesn't matter if an object is nested or not; to encode any object that isn't directly mapped to a JSON type you'll need to write additional code to handle the conversion. — Martijn Pieters
– Martijn Pieters, Commented Aug 21, 2014 at 11:15
Ok, which code is it? I prefer it will be a method I need ti implement in the object and outside it because I have another place that calls json,dumps on any object it gets — Tal Barda
– Tal Barda, Commented Aug 21, 2014 at 11:30

Kasravnd · Accepted Answer · 2014-08-21 22:10:13Z

0

You can use subclass JSONEncoder and implement your own custom serialization.so use this code :

from json import JSONEncoder

class leaf_object(object):
    def __init__(self, s):
        self.value = s

class nested_object(object):
    def __init__(self, a, b_list):
        self.a = a
        self.b_list = b_list

class MyEncoder(JSONEncoder):
    def default(self, o):
        return o.__dict__
if __name__ == "__main__":
    obj = nested_object('a1', [leaf_object('a1.1'),leaf_object('a1.2')])
    obj=MyEncoder().encode(obj)
    import json
    print(json.dumps(obj))

this is the result:

"{\"a\": \"a1\", \"b_list\": [{\"value\": \"a1.1\"}, {\"value\": \"a1.2\"}]}"

edited Aug 21, 2014 at 22:10

answered Aug 21, 2014 at 11:53

Kasravnd

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2 Comments

Tal Barda Over a year ago

I wasn't clear - I'm trying to avoid the changing of the json.dumps by changing the nested/leaf_object objects code BTW, you can in your suggestion you can use the json dumps tis way : print(json.dumps(obj,cls=MyEncoder))

Kasravnd Over a year ago

why you dont want to change json.dump ? so you can change the obj before, as i update the answer ?... if you want another ways you can see similar questions !

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