CODEWITHSUNDEEP
pythonjsonclass-method
Boyan Kushlev
Boyan Kushlev

Reputation: 1053

Create an object from a JSON file in python (using a classmethod)?

I wanna create a classmethod that takes a JSON (dictionary) string and creates an instance of the class it's called on. For example, if I have a class Person the inherits from a class Jsonable with age and name:

class Person(Jsonable):
    def __init__(self, name, age):
        self.name = name
        self.age = age
class Jsonable:
    @classmethod
    def from_json(json_string):
        # do the magic here

and if I have a JSON string string = "{'name': "John", 'age': 21}" and when I say person1 = Person.from_json(string) I want to create person1 with name John and age 21. I also have to keep the class name in some way so that when I call for example Car.from_json(string) it raises a TypeError.

Upvotes: 2

Views: 3377

Answers (1)

Andrii Rusanov
Andrii Rusanov

Reputation: 4606

it supposes you have a key __class in you JSON string that holds target class name

import json

class Jsonable(object):
    @classmethod
    def from_json(cls, json_string):
        attributes = json.loads(json_string)
        if not isinstance(attributes, dict) or attributes.pop('__class') != cls.__name__:
            raise ValueError
        return cls(**attributes)

Upvotes: 3

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