python json object array not serializable

Question

I have a class and array in a loop. I'm filling the object and appending it to the array. How do I pass array data to web side through JSON? I have an error that says JSON is not serializable. How can I serialize to a JSON?

class myclass(object):
    def __init__(self,vehicle,mng01):
        self.vehicle = vehicle
        self.vehicle = vehicle

#--Main function--
@subApp.route('/jsontry', method=['POST'])
def data():
    for x in list:
        vehicle_sum.append(myclass( x,str(mng01))

    return json.dumps({'success':'1','vehicle':vehicle_sum})

Can you post the error stack please ? When I try to dump `{'success':'1','vehicle':vehicle_sum}` with `vehicle_sum` being a standard python array, it works. Please provide more details regarding the error and the objects you use :) — Floran Gmehlin, Oct 03 '16 at 09:15
@FloranGmehlin: It is a list, of instances of `myclass`. This will not work out of the box. See my answer below :) — UltraInstinct, Oct 03 '16 at 09:19
Why do you have two `self.vehicle = vehicle` statements in `myclass.__init__()`? — martineau, Oct 03 '16 at 09:47
See this [answer](http://stackoverflow.com/a/18561055/355230) to a related question. — martineau, Oct 03 '16 at 09:49

score 4 · Answer 1 · answered Oct 03 '16 at 09:16

Does it say myclass object is not JSON serializable? This is because there is no way for json.dumps(..) to know how to JSON-serialize your class. You will need to write your custom encoder to do that.

Below is a sample implementation. I am sure you can modify it for your use case.

import json

class Temp(object):
    def __init__(self, num):
        self.num = num

class CustomEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Temp):
            return {"num": obj.num}
        #Let the base class handle the problem.
        return json.JSONEncoder.default(self, obj)

obj = [Temp(42), Temp(42)]


print json.dumps(obj, cls=CustomEncoder)

#Output: [{"num": 42}, {"num": 42}]

If you don't want over-complicate stuff, here's what you can do:

all_vehicles = [{"vehicle": x.vehicle} for x in vehicle_sum]
json.dumps({'success':'1','vehicle':all_vehicles)

I get `An attribute defined in json.encoder line 162 hides this method `, it happens on the line `def default(self, obj):` but the code still works. — clankill3r, Jan 30 '19 at 09:20

score 0 · Answer 2 · edited May 23 '17 at 12:00

It doesn't say that JSON is not serializable, it says that your instances of myclass are not JSON serializable. I.e. they cannot be represented as JSON, because it is really not clear what do you expect as an output.

To find out how to make a class JSON serializable, check this question: How to make a class JSON serializable

In this trivial case, depending on what exactly you're trying to achieve, you might be good with inserting [x.vehicle for x in vehicle_sum] in your JSON. If you really need to insert your instances data in JSON in a direct way, you'll have to write an encoder.

python json object array not serializable

2 Answers2

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