Python class to json string

Problem

Sometimes you need to convert a python class into a json string.

Solution

There are a lot of different ways of doing it, but one that I normally use is by defining the following method in the class:

import json

class ...:

...

def to_json(self):
    return json.dumps(self, default=lambda o: dict((key, value) for key, value in o.__dict__.items() if value), sort_keys=True, allow_nan=False, indent=False)

As you can see there are a few options for configuring the json.dumps method, some of the most interesting:

• sort_keys: to order the json fields alphabetically.
• allow_nan: to include nulls / None fields.
• indent: to pretty print the json.

Example

A full example:

import json

class Person:

    def __init__(self, name, surname, age):
        self.name = name
        self.surname = surname
        self.age = age

    def __str__(self):
        return f"Person(name='{self.name}', surname='{self.surname}', age={self.age})"

    def to_json(self):
        return json.dumps(self, default=lambda o: dict((key, value) for key, value in o.__dict__.items() if value), sort_keys=True, allow_nan=False)

if __name__ == '__main__':
    p1 = Person("Name", "Surname", 10)
    print(p1)
    print(p1.to_json())

Which prints the following on the console:

# print(p1)
Person(name='Name', surname='Surname', age=10)

# print(p1.to_json())
{"age": 10, "name": "Name", "surname": "Surname"}

Example with nested structures

This approach also works with nested structures:

import json


class Job:
    def __init__(self, name):
        self.jobName = name

class Person:

    def __init__(self, name, surname, age, jobs):
        self.name = name
        self.surname = surname
        self.age = age
        self.jobs = jobs

    def to_json(self):
        return json.dumps(self, default=lambda o: dict((key, value) for key, value in o.__dict__.items() if value), sort_keys=True, allow_nan=False)

if __name__ == '__main__':
    p1 = Person("Name", "Surname", 10, [Job("Teacher")])
    print(p1.to_json())

{"age": 10, "jobs": [{"jobName": "Teacher"}], "name": "Name", "surname": "Surname"}