Convert Simple JSON to a Python Dataclass

From JSON to a Python Dataclass

The simplest conversion turns a flat JSON object into a Python @dataclass. Each JSON key becomes a field with a type annotation inferred from the value.

Example JSON

{
  "id": 42,
  "name": "Alice",
  "email": "alice@example.com",
  "active": true,
  "score": 98.5
}

Generated Python

from dataclasses import dataclass

@dataclass
class User:
    id: int
    name: str
    email: str
    active: bool
    score: float

Type Mapping Rules

JSON type	Python type
string	str
number (integer)	int
number (decimal)	float
boolean	bool
null	None

Python distinguishes between int and float, so 42 maps to int while 98.5 maps to float. This is more precise than languages like TypeScript that use a single number type.

Why Dataclasses?

Dataclasses (introduced in Python 3.7) provide:

• Auto-generated __init__ — No boilerplate constructor needed.
• __repr__ and __eq__ — Useful for debugging and testing.
• Type annotations — IDE autocompletion and static analysis with mypy or pyright.
• Immutability option — Set frozen=True to prevent accidental mutation.

Usage

import json

data = json.loads('{"id": 42, "name": "Alice", "email": "alice@example.com", "active": true, "score": 98.5}')
user = User(**data)
print(user.name)  # "Alice"

A simple dataclass is the foundation for all JSON-to-Python conversions. Once you understand this pattern, nested objects, optional fields, and complex structures follow naturally.