The built-in json module of Python can only handle Python primitives types that have a direct JSON equivalent. i.e., The fundamental problem is that the JSON encoder json.dump() and json.dumps() only knows how to serialize the basic set of object types by default (e.g., dictionary, lists, strings, numbers, None, etc.). To solve this, we need to build a custom encoder to make our Class JSON serializable.

Sample Code:

import json
 class Employee(dict):
    def __init__(self, name, age, salary, address):
        dict.__init__(self, name=name, age=age, salary=salary, address=address)
 class Address(dict):
    def __init__(self, city, street, pin):
        dict.__init__(self, city=city, street=street, pin=pin)
 address = Address("Alpharetta", "7258 Spring Street", "30004")
employee = Employee("John", 36, 9000, address)
 print("Encode into JSON formatted Data")
employeeJSON = json.dumps(employee)
print(employeeJSON)
 # Let's load it using the load method to check if we can decode it or not.
print("Decode JSON formatted Data")
employeeJSONData = json.loads(employeeJSON)
print(employeeJSONData)

Output:

Encode into JSON formatted Data
{"name": "John", "age": 36, "salary": 9000, "address": {"city": "Alpharetta", "street": "7258 Spring Street", "pin": "30004"}}
 Decode JSON formatted Data
{'name': 'John', 'age': 36, 'salary': 9000, 'address': {'city': 'Alpharetta', 'street': '7258 Spring Street', 'pin': '30004'}}