How to convert JSON into instances of a custom class?

Question

I am not sure if this question has been asked before but I can't find related custom mapping. Usually it is a direct JSON to object 1:1 mapping.

So here is my sample example:

class Test():
    id: str
    name: str
    msg: str

data = [
    {
        "id": "12345",
        "client": "test",
        "msg": "random"
    }, {
        "id": "54321",
        "client": "test-2",
        "msg": "random-2"
    }
]

So on above I have a JSON, I wanted to directly convert it to object I have on the first class. Note the "client" from the JSON becomes name.

So the final output when I do load the object it would become.

data = [
    {
        "id": "12345",
        "name": "test",
        "msg": "random"
    }, {
        "id": "54321",
        "name": "test-2",
        "msg": "random-2"
    }
]

Your class doesn't do anything. Should it be a dataclass? And where do you think the mapping client -> name comes from? — jonrsharpe
– jonrsharpe, Commented Jun 3, 2021 at 17:59
sorry I am fairly new to python coming from java background. what I was trying to do was create an custom object and have json mapped to that custom class. — logger
– logger, Commented Jun 3, 2021 at 18:01
It's not clear what you actually tried to implement that. Python will deserialize the JSON to a list of dicts, if you want something else you have to customise the process or convert it afterwards. — jonrsharpe
– jonrsharpe, Commented Jun 3, 2021 at 18:03
Is your json correct? Test has a "name" property but the json in data has "client" istead of "name" — daniboy000
– daniboy000, Commented Jun 3, 2021 at 18:08
And note that if your class doesn't have any behaviour you don't need to do this at all - Python isn't Java, you can often just stick with a dictionary. — jonrsharpe
– jonrsharpe, Commented Jun 3, 2021 at 18:19

Rafael Setton · Accepted Answer · 2021-06-03 18:02:05Z

3

class Test():
    def __init__(self, id, client, msg):
        self.id = id
        self.name = client
        self.msg = msg

data = [
    {
        "id": "12345",
        "client": "test",
        "msg": "random"
    }, {
        "id": "54321",
        "client": "test-2",
        "msg": "random-2"
    }
]

# unpack values from dict and pass in as arguments for Test.__init__()
objects = [Test(**item) for item in data]

answered Jun 3, 2021 at 18:02

Rafael Setton

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4 Comments

jonrsharpe Over a year ago

I don't think it makes sense to encode that mapping client parameter -> name attribute in the initialiser, what about when you create instances that aren't from that JSON? Typically you'd do this as a class method, e.g. Test.from_dict(item).

Rafael Setton Over a year ago

The questions says that it should map from THIS JSON format. For other formats, it would need a different class.

jonrsharpe Over a year ago

If it was only for that JSON why would it need to rename a property? And would you really write multiple implementations of the same class for different sources? That seems like a bit of a smell.

jonrsharpe Over a year ago

Here's a good example of a healthier pattern: stackoverflow.com/a/30114013/3001761

daniboy000 · Accepted Answer · 2021-06-03 19:00:44Z

2

You can use Pydantic as well to define your class like showed bellow:

from pydantic import BaseModel

class User(BaseModel):
    id: str
    name: str
    msg: str

    def __init__(self, id: str, client: str, msg: str) -> None:
        super().__init__(id=id, name=client, msg=msg)

users = [
    {
        'id': '12345',
        'client': 'test',
        'msg': 'random',
    },
    {
        'id': '54321',
        'client': 'test-2',
        'msg': 'random-2',
    }
]

objects = [User(**user) for user in users]

print(objects)
# Output
[
   User(id='12345', name='test', msg='random'),
   User(id='54321', name='test-2', msg='random-2')
]

edited Jun 3, 2021 at 19:00

answered Jun 3, 2021 at 18:19

daniboy000

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2 Comments

logger Over a year ago

this would only be fine but the problem is that response is returning "client" and I want to mapped to "name"

daniboy000 Over a year ago

My bad. Updated the code in order to read the correct json.

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