python-attrs / python-attrs/attrs

Way to specify KW_ONLY location in the constructor like in dataclass.KW_ONLY

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dataclasses Feature
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Python
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Description

dataclass in python 3.10 and above got KW_ONLY sentinel value
it allows you to mark where the constructor will start the KWARGS in the class
https://docs.python.org/3/library/dataclasses.html#dataclasses.KW_ONLY
i did not found a way to do this in attrs package

@dataclass()
class Foo():
    x:str=field(default="a")
    _:KW_ONLY
    y:bool

the function signature of the init will be

(x: str = "a", *, y: bool) -> None

the dataclass one will re order the items order in the constructor and handle inheritance properly(if needed)

https://docs.python.org/3/library/dataclasses.html#re-ordering-of-keyword-only-parameters-in-init

from dataclasses import dataclass,KW_ONLY,field

@dataclass
class Base:
    x: float = 15.0
    _: KW_ONLY
    y: int = 0
    w: int = 1

@dataclass
class D(Base):
    z: int = 10
    _: KW_ONLY
    t: int = field(kw_only=False, default=0)

function signature:

(x: float = 15, z: int = 10, t: int = 0, *, y: int = 0, w: int = 1) -> None

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Use the linked Python dataclasses.KW_ONLY documentation and the two examples as the behavioral reference. Inspect attrs' constructor generation and existing keyword-only and inheritance tests; done means attrs can express the requested marker behavior, preserves the shown constructor ordering, and has coverage for both examples.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
developer-experience
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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