Dataclasses

from dataclasses import dataclass, field
from typing import List

# Basic dataclass
@dataclass
class Point:
    x: float
    y: float

p1 = Point(3, 4)
p2 = Point(3, 4)
print(p1)           # Point(x=3, y=4)
print(p1 == p2)     # True (auto __eq__!)

# With defaults and methods
@dataclass
class User:
    name: str
    email: str
    age: int = 0
    active: bool = True
    tags: List[str] = field(default_factory=list)
    
    def greet(self):
        return f"Hello, {self.name}!"

user = User("Alice", "alice@email.com", 25)
user.tags.append("python")
print(user)
print(user.greet())

# Frozen (immutable) dataclass
@dataclass(frozen=True)
class Config:
    host: str = "localhost"
    port: int = 8080
    debug: bool = False

config = Config()
print(config)
# config.port = 3000  # FrozenInstanceError!

# Ordered dataclass
@dataclass(order=True)
class Student:
    gpa: float
    name: str = field(compare=False)

students = [Student(3.8, "Alice"), Student(3.5, "Bob"), Student(3.9, "Charlie")]
for s in sorted(students):
    print(f"  {s.name}: {s.gpa}")

# Post-init processing
@dataclass
class Product:
    name: str
    price: float
    quantity: int
    total: float = field(init=False)
    
    def __post_init__(self):
        self.total = self.price * self.quantity

product = Product("Widget", 9.99, 5)
print(f"{product.name}: ${product.total:.2f}")