kw_only doesn't work with mypy

[quinor]

Use mypy on following file:

import typing
import attr


@attr.s(frozen=True, auto_attribs=True, kw_only=True)
class Position:
    line: int
    column: int


@attr.s(frozen=True, auto_attribs=True, kw_only=True)
class Node:
    start: typing.Optional[Position] = None
    end: typing.Optional[Position] = None


@attr.s(frozen=True, auto_attribs=True, kw_only=True)
class Operator(Node):
    symbol: str
    name: str
    precedence: int
    associativity: str  # "left" or "right"

It gives following errors:

f.py:21: error: Non-default attributes not allowed after default attributes.
f.py:22: error: Non-default attributes not allowed after default attributes.
f.py:23: error: Non-default attributes not allowed after default attributes.
f.py:24: error: Non-default attributes not allowed after default attributes.

If I understand correctly, mypy doesn't consider the existence of a new kw_only=True .

[euresti]

Hmm. This feature definitely didn't exist when I wrote the plugin. Maybe I'll have time over the break to work on this.

[quinor]

From my understanding it makes mypy unusable with attrs right now, or is there a workaround that doesn't require too much code?

[euresti]

Sadly, for now the only way around it is to # type: ignore those lines.

[hynek]

This should be a bug on the mypy tracker no?

[dmfigol]

@euresti
thanks for the mypy plugin!
The latest Pycharm 2018.3.2 still does not like kw_only. Inspection throws an error on the decorator line and whenever an object is created:

1. Code: @attr.s(auto_attribs=True, repr=False, kw_only=True)
   Pycharm inspection:

Unexpected argument(s). Possible callees: attrs(maybe_cls: None=..., these: Optional[Dict[str, Any]]=..., repr_ns: Optional[str]=..., repr: bool=..., cmp: bool=..., hash: Optional[bool]=..., init: bool=..., slots: bool=..., frozen: bool=..., str: bool=..., auto_attribs: bool=...) attrs(maybe_cls: _C, these: Optional[Dict[str, Any]]=..., repr_ns: Optional[str]=..., repr: bool=..., cmp: bool=..., hash: Optional[bool]=..., init: bool=..., slots: bool=..., frozen: bool=..., str: bool=..., auto_attribs: bool=...)

2. Code: Car(name="Lotus", year=2001) # object created with attrs + kw_only
   Pycharm inspection:
   Unexpected argument(s). Possible callees: object(self: object) object.__new__(cls: object)

It seems that attrs stub in typeshed is missing kw_only?
.../typeshed/third_party/2and3/attr/__init__.pyi

@overload
def attrs(maybe_cls: _C,
          these: Optional[Dict[str, Any]] = ...,
          repr_ns: Optional[str] = ...,
          repr: bool = ...,
          cmp: bool = ...,
          hash: Optional[bool] = ...,
          init: bool = ...,
          slots: bool = ...,
          frozen: bool = ...,
          str: bool = ...,
          auto_attribs: bool = ...) -> _C: ...
@overload
def attrs(maybe_cls: None = ...,
          these: Optional[Dict[str, Any]] = ...,
          repr_ns: Optional[str] = ...,
          repr: bool = ...,
          cmp: bool = ...,
          hash: Optional[bool] = ...,
          init: bool = ...,
          slots: bool = ...,
          frozen: bool = ...,
          str: bool = ...,
          auto_attribs: bool = ...) -> Callable[[_C], _C]: ...

UPDATE: it seems it is already fixed in the typeshed. I didn't notice, sorry

[euresti]

Fixed here:
python/typeshed#2720
And here:
python/mypy#6107