object not json serializable

Question

While coding in python I'm getting an error: "Object of type myObject is not JSON serializable"

I tried to use some solutions I saw in other questions, but I didn't find many similarities between my code and the code in those questions, so I found it difficult to adapt the solutions in my code.

A part of my script is as follows. The error occurs in the last line of the first block:

import json
import os
from my_object import myObject

for a in A_set:
    if os.path.isfile(filename):
        with open(filename, 'r') as f:
            json_data = json.load(f)
        object_name = myObject.from_json(json_data)
    else:
        object_name = myObject(a)
        object_name.property_A = property_A
        object_name.property_C = []

    object_name.property_C_add_elements(var)
    with open(filename, 'w') as f:
        json.dump(object_name.to_json(), f)

In another python file is defined the class of 'myObject', where is also the method 'to_json()', which I'm calling in the line of code that produces the error.

class myObject:
    def __init__(self, name):
        self.name = name
        self.property_A = property_A
        self.property_B = property_B
        self.property_C = []

    def property_C_add_elements(self, var):  
        self.property_C.append(var)

    def to_json(self):
        return {
            'Name': self.name,
            'property A': self.property_A,
            'property B': self.property_B,
            'property C': self.property_C
        }

    @classmethod
    def from_json(cls, jason_data):
        object_name = myObject(jason_data['property A'])
        property_B = myObject(jason_data['property B'])
        c_list = []
        for var in jason_data['property C']:
            c_list.append(myObject(var))

        object_name.property_B = property_B
        object_name.property_C = c_list

        return object_name

I would be glad if I could get a solution to that problem. Thanks in advance.

Chgad · Accepted Answer

from the code you provided i can only speculate what types exactly your property_A, property_B, property_C variables/attributes are but

@classmethod
def from_json(cls, jason_data):
    object_name = myObject(jason_data['property A'])
    property_B = myObject(jason_data['property B'])
    c_list = []
    for var in jason_data['property C']:
        c_list.append(myObject(var))

    object_name.property_B = property_B
    object_name.property_C = c_list

    return object_name

Let's me speculate that your properties are Classinstances which have no "definition" of how they should be serialized into JSON. This is backed up by what you said :

"Object of type myObject is not JSON serializable"

I guess the problem is with the from_json() classmethod, there you should probably do smth. like :

EDITED:

Assuming that the __init__() method of your Class looks as follows

def __init__(self, name, property_A, property_B, property_C):
    self.name = name
    self.property_A = property_A
    self.property_B = property_B
    self.property_C = property_C 
    # property_C should be a list, you may want to add validation method 
    # which checks for correct types if it is preocess cirtical

I suggest the following:

@classmethod
def from_json(cls, jason_data):
    return cls(
               jason_data['name'],
               jason_data['property A'],
               jason_data['property B'],
               jason_data['property C']
               )

Furthermore i suggest, if it's possible, that you change your JSON Format, provided in your to_json() method by simply replacing the whitespaces from "property A" to "property_A" (same for other properties). In addition you can change "Name" to lowercase "name".

Why ? Because with this format, and my changed __init__() method you can convert your from_json() to the following utilizing unpacking operation :

@classmethod
def from_json(cls, jason_data):
    return cls(**json_data)

object not json serializable

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