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## Summary https://github.com/astral-sh/ty/issues/111 adds support for `@dataclass(kw_only=True)` (https://docs.python.org/3/library/dataclasses.html) ## Test Plan - new mdtests - triaged conformance diffs (notes here: https://diffswarm.dev/d-01k2gknwyq82f6x17zqf3apjxc) - `mypy_primer` no-op
2.1 KiB
2.1 KiB
Dataclass fields
Basic
from dataclasses import dataclass, field
@dataclass
class Member:
name: str
role: str = field(default="user")
tag: str | None = field(default=None, init=False)
# revealed: (self: Member, name: str, role: str = Literal["user"]) -> None
reveal_type(Member.__init__)
alice = Member(name="Alice", role="admin")
reveal_type(alice.role) # revealed: str
alice.role = "moderator"
# `tag` is marked as `init=False`, so this is an
# error: [unknown-argument] "Argument `tag` does not match any known parameter"
bob = Member(name="Bob", tag="VIP")
default_factory
The default_factory argument can be used to specify a callable that provides a default value for a
field:
from dataclasses import dataclass, field
from datetime import datetime
@dataclass
class Data:
content: list[int] = field(default_factory=list)
timestamp: datetime = field(default_factory=datetime.now, init=False)
# revealed: (self: Data, content: list[int] = list[Unknown]) -> None
reveal_type(Data.__init__)
data = Data([1, 2, 3])
reveal_type(data.content) # revealed: list[int]
reveal_type(data.timestamp) # revealed: datetime
kw_only
[environment]
python-version = "3.12"
If kw_only is set to True, the field can only be set using keyword arguments:
from dataclasses import dataclass, field
@dataclass
class Person:
name: str
age: int | None = field(default=None, kw_only=True)
role: str = field(default="user", kw_only=True)
# revealed: (self: Person, name: str, *, age: int | None = None, role: str = Literal["user"]) -> None
reveal_type(Person.__init__)
alice = Person(role="admin", name="Alice")
# error: [too-many-positional-arguments] "Too many positional arguments: expected 1, got 2"
bob = Person("Bob", 30)
The field function
from dataclasses import field
def get_default() -> str:
return "default"
reveal_type(field(default=1)) # revealed: dataclasses.Field[Literal[1]]
reveal_type(field(default=None)) # revealed: dataclasses.Field[None]
reveal_type(field(default_factory=get_default)) # revealed: dataclasses.Field[str]