dataclass: các lớp dữ liệu không có bản soạn sẵn

class Punto:
    def __init__(self, x: float, y: float) -> None:
        self.x = x
        self.y = y
    def __repr__(self) -> str:
        return f"Punto(x={self.x}, y={self.y})"
    def __eq__(self, other) -> bool:
        if not isinstance(other, Punto):
            return NotImplemented
        return (self.x, self.y) == (other.x, other.y)

from dataclasses import dataclass

@dataclass
class Punto:
    x: float
    y: float

p = Punto(3, 4)
p             # Punto(x=3, y=4)   ← __repr__ gratis
Punto(3, 4) == Punto(3, 4)        # True ← __eq__ gratis
p.x, p.y      # 3, 4

from dataclasses import dataclass, field

@dataclass
class Articolo:
    nome: str
    prezzo: float = 0.0
    tag: list[str] = field(default_factory=list)

@dataclass(frozen=True)
class Coordinata:
    lat: float
    lon: float

c = Coordinata(45.4, 9.2)
c.lat = 99   # FrozenInstanceError!

@dataclass(order=True)
class Voto:
    valore: int

Voto(10) < Voto(20)   # True
sorted([Voto(30), Voto(10), Voto(20)])

import math
from dataclasses import dataclass

@dataclass
class Punto:
    x: float
    y: float
    def distanza_dall_origine(self) -> float:
        return math.hypot(self.x, self.y)

Punto(3, 4).distanza_dall_origine()   # 5.0