Dataclasses

from dataclasses import dataclass

@dataclass
class Point:
    x: float
    y: float

# __init__ auto-generated
p1 = Point(3.0, 4.0)
p2 = Point(3.0, 4.0)

# __repr__ auto-generated
print(p1)  # Point(x=3.0, y=4.0)

# __eq__ auto-generated
print(p1 == p2)  # True

from dataclasses import dataclass, field
from typing import List

@dataclass
class Student:
    name: str
    grades: List[float] = field(default_factory=list)
    active: bool = True
    year: int = 1

s = Student("Alice")
print(s)  # Student(name='Alice', grades=[], active=True, year=1)

from dataclasses import dataclass

@dataclass(frozen=True)
class Config:
    host: str
    port: int = 5432

cfg = Config("localhost")
# cfg.port = 8080  # FrozenInstanceError!

from dataclasses import dataclass, field

@dataclass
class Product:
    name: str
    price: float
    quantity: int = 0

    # Computed field — not in __init__
    @property
    def total_value(self) -> float:
        return self.price * self.quantity

    # Post-init processing
    def __post_init__(self):
        if self.price < 0:
            raise ValueError("Price cannot be negative")

from dataclasses import dataclass

@dataclass
class Person:
    name: str
    age: int

@dataclass
class Employee(Person):
    employee_id: str
    department: str = "Engineering"

emp = Employee("Alice", 30, "E001")
print(emp)  # Employee(name='Alice', age=30, employee_id='E001', department='Engineering')

from dataclasses import dataclass

@dataclass(order=True)
class Priority:
    level: int
    description: str = field(compare=False)  # exclude from comparison

tasks = [Priority(3, "low"), Priority(1, "high"), Priority(2, "medium")]
sorted_tasks = sorted(tasks)  # Sorted by level
print([t.level for t in sorted_tasks])  # [1, 2, 3]

from dataclasses import dataclass, asdict, astuple
import json

@dataclass
class User:
    name: str
    email: str
    age: int

user = User("Alice", "alice@example.com", 30)

# To dict
print(asdict(user))
# {'name': 'Alice', 'email': 'alice@example.com', 'age': 30}

# To tuple
print(astuple(user))
# ('Alice', 'alice@example.com', 30)

# To JSON
print(json.dumps(asdict(user)))
# {"name": "Alice", "email": "alice@example.com", "age": 30}