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## Summary
Add basic support for `dataclasses.field`:
* remove fields with `init=False` from the signature of the synthesized
`__init__` method
* infer correct default value types from `default` or `default_factory`
arguments
```py
from dataclasses import dataclass, field
def default_roles() -> list[str]:
return ["user"]
@dataclass
class Member:
name: str
roles: list[str] = field(default_factory=default_roles)
tag: str | None = field(default=None, init=False)
# revealed: (self: Member, name: str, roles: list[str] = list[str]) -> None
reveal_type(Member.__init__)
```
Support for `kw_only` has **not** been added.
part of https://github.com/astral-sh/ty/issues/111
## Test Plan
New Markdown tests
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)
# TODO: the `age` and `role` fields should be keyword-only
# revealed: (self: Person, name: str, age: int | None = None, role: str = Literal["user"]) -> None
reveal_type(Person.__init__)
alice = Person(role="admin", name="Alice")
# TODO: this should be an error
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]