@dataclass: классы без бойлерплейта

class ProductManual:
    def __init__(self, name, price):
        self.name = name
        self.price = price

    def __repr__(self):
        return f"Product(name={self.name!r}, price={self.price!r})"

    def __eq__(self, other):
        if not isinstance(other, ProductManual):
            return NotImplemented
        return (self.name, self.price) == (other.name, other.price)

from dataclasses import dataclass

@dataclass
class Product:
    name: str
    price: int

a = Product("кружка", 350)
b = Product("кружка", 350)
print(a)
print(a == b)

Product(name='кружка', price=350)
True

from dataclasses import dataclass

@dataclass
class Product:
    name: str
    price: int = 100
    in_stock: bool = True

print(Product("степлер"))
print(Product("точилка", 80))

Product(name='степлер', price=100, in_stock=True)
Product(name='точилка', price=80, in_stock=True)

from dataclasses import dataclass, field

@dataclass
class Order:
    number: int
    items: list = field(default_factory=list)
    tags: list = field(default_factory=list)

    def add(self, item):
        self.items.append(item)

o1 = Order(1)
o2 = Order(2)
o1.add("ручка")
o1.tags.append("срочно")

print(o1)
print(o2)

Order(number=1, items=['ручка'], tags=['срочно'])
Order(number=2, items=[], tags=[])

from dataclasses import dataclass

@dataclass(frozen=True)
class Point:
    x: int
    y: int

p = Point(2, 3)

print(p in {Point(2, 3), Point(4, 1)})
print(len({Point(2, 3), Point(2, 3)}))

try:
    p.x = 10
except Exception as e:
    print(type(e).__name__)

True
1
FrozenInstanceError

from dataclasses import dataclass, field

@dataclass
class Rectangle:
    width: int
    height: int
    area: int = field(init=False)

    def __post_init__(self):
        self.area = self.width * self.height

r1 = Rectangle(3, 4)
r2 = Rectangle(5, 5)
print(r1)
print(r2.area)

Rectangle(width=3, height=4, area=12)
25