Bradley Kirton's Blog

Published on June 22, 2023

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Simple object mapping using the built in json module in Python

Today I learned about the object_hook input to the json.loads and json.load methods. I discovered this while reading this github issue.

The example referenced in the issue makes use of the SimpleNamespace object.

import json
import types

order = json.loads(
    '{"ref": "ORD1234", "price": 1.35}',
    object_hook=lambda x: types.SimpleNamespace(**x),
order  # namespace(ref='ORD1234', price=1.35)

This is a really cool feature I wished I had discovered earlier. For those instances where reaching for something like pydantic seems overkill, maybe something like this could be useful.

import json
import dataclasses

class Order:
    ref: str
    price: float

    def from_dict(cls, data: dict[str, str | float]) -> "Order":
        ref = data["ref"]
        price = data["price"]
        return cls(ref=ref, price=price)

order = json.loads(
    '{"ref": "ORD1234", "price": 1.35}',
order  # Order(ref='ORD1234', price=1.35)