Why is this class not JSon serializable?

Question

I have this class in Python 3.5:

class DataPoint(object):

    def __init__(self, time, value):
        self.time = time
        self.value = value

And when I try to create a JSon from an instance, doing:

json.dumps( intance_of_datapoint )

I get the error:

TypeError: < DataPoint object at 0x0123 > is not JSon Serializable

So I have tried to improve the class overwritting the repr method, like this:

class DataPoint(object):

    def __init__(self, time, value):
        self.time = time
        self.value = value

    def __str__(self):
        return json.dumps(self.__dict__)

    __repr__ = __str__

By doing that I get:

TypeError: {"value":52.29, "time":1} is not JSon serializable.

Can you guys helps me undestand why? I'm pretty lost here.

score 4 · Accepted Answer · answered Nov 28 '17 at 14:07

4

You will need to convert your instance in python dict and then you can dump that dict in json.dumps(instance_dict). because, as json have its own data types, and python user defined class cannot serialize to json.

answered Nov 28 '17 at 14:07

Akash Wankhede

618
6
15

That did the trick! I wonder why the Json encoder doesn't do the job and call ._ _dict_ _ for every object it finds. – cgajardo Nov 28 '17 at 15:56
You can upvote my answer if it helps you. – Akash Wankhede Nov 28 '17 at 16:10

Why is this class not JSon serializable?

1 Answers1