dataclasses and __slots__

Detailed answer

Logic: @dataclass auto-generates __init__, __repr__, __eq__. slots=True (Py3.10+) fixes attributes and saves memory. frozen=True makes instances hashable if all fields hashable. Complexity notes included in code section when present. Pros: Less boilerplate than manual classes; slots reduce per-instance dict overhead. Cons: Inheritance with slots tricky; default mutable fields need default_factory. Core: @dataclass auto-generates __init__, __repr__, __eq__. slots=True (Py3.10+) fixes attributes and saves memory. frozen=True makes instances hashable if all fields hashable. Real-time example: DTO layer: @dataclass(slots=True) OrderItem(sku: str, qty: int, price: Decimal). Pros: Less boilerplate than manual classes; slots reduce per-instance dict overhead. Cons: Inheritance with slots tricky; default mutable fields need default_factory. Common mistakes: Mutable default list in dataclass field; forgetting frozen for dict keys. Best practices: Use field(default_factory=list); kw_only=True for clarity in large models. Audience level: Fresher.

Full explanation

@dataclass auto-generates __init__, __repr__, __eq__. slots=True (Py3.10+) fixes attributes and saves memory. frozen=True makes instances hashable if all fields hashable.

Code example

from dataclasses import dataclass, field

@dataclass(slots=True, frozen=True)
class Point:
    x: float
    y: float

@dataclass
class Cart:
    items: list[str] = field(default_factory=list)

    def add(self, sku: str) -> None:
        self.items.append(sku)

Practice code · python (view only · no execution)

from dataclasses import dataclass, field

@dataclass(slots=True, frozen=True)
class Point:
    x: float
    y: float

@dataclass
class Cart:
    items: list[str] = field(default_factory=list)

    def add(self, sku: str) -> None:
        self.items.append(sku)