ruff/crates/ty_python_semantic/resources/mdtest/external/attrs.md

attrs

[environment]
python-version = "3.13"
python-platform = "linux"

[project]
dependencies = ["attrs==25.4.0"]

Basic class (attr)

import attr

@attr.s
class User:
    id: int = attr.ib()
    name: str = attr.ib()

user = User(id=1, name="John Doe")

reveal_type(user.id)  # revealed: int
reveal_type(user.name)  # revealed: str

Basic class (define)

from attrs import define, field

@define
class User:
    id: int = field()
    internal_name: str = field(alias="name")

user = User(id=1, name="John Doe")
reveal_type(user.id)  # revealed: int
reveal_type(user.internal_name)  # revealed: str

Usage of field parameters

from attrs import define, field

@define
class Product:
    id: int = field(init=False)
    name: str = field()
    price_cent: int = field(kw_only=True)

reveal_type(Product.__init__)  # revealed: (self: Product, name: str, *, price_cent: int) -> None

Dedicated support for the default decorator?

We currently do not support this:

from attrs import define, field

@define
class Person:
    id: int = field()
    name: str = field()

    # error: [call-non-callable] "Object of type `_MISSING_TYPE` is not callable"
    @id.default
    def _default_id(self) -> int:
        raise NotImplementedError

# error: [missing-argument] "No argument provided for required parameter `id`"
person = Person(name="Alice")
reveal_type(person.id)  # revealed: int
reveal_type(person.name)  # revealed: str