dataclasses kw_only doesn't seem to allow mixing defaults and inheritance

[KerryCerqueira]

Since pull request #413 using a dataclass annotation with the kw_only flag "works as expected", but if I declare classes like

from serde import serde, field
from dataclasses import dataclass


@serde
@dataclass(kw_only=True)
class Foo:
    x: int = field(default=0)


@serde
@dataclass(kw_only=True)
class Bar(Foo):
    y: int

python throws a familiar error about the order of constructor arguments. I didn't find any examples in the documentation using inheritance so it's not clear to me how this feature is supported, or what I'm supposed to do to once-and-for-all set all relevant fields to be keyword only. If this works, can anyone help me with a minimal example of correct usage?

[yukinarit]

Hi @KerryCerqueira
This worked for me. Can you share the complete reproducible code?

from serde import serde, field
from serde.json import to_json, from_json
from dataclasses import dataclass

@serde
@dataclass(kw_only=True)
class Foo:
    x: int = field(default=0)

@serde
@dataclass(kw_only=True)
class Bar(Foo):
    y: int

if __name__ == "__main__":
    y = Bar(y=10)
    xy = Bar(y=10, x=20)
    print(y)
    print(xy)
    print(to_json(xy))
    print(from_json(Foo, '{"y": 10, "x": 20}'))

Bar(x=0, y=10)
Bar(x=20, y=10)
{"x":20,"y":10}
Foo(x=20)

[KerryCerqueira]

You're right, both my example and yours do work. I'd convinced myself somehow that the interpreter was throwing the error but now when I try it only pyright does:

...test.py:13:5 - error: Fields without default values cannot appear after fields with default values (reportGeneralTypeIssues)

That's still a little confusing though. Any idea why the static analysis is failing?

[yukinarit]

I guess this is relevant? microsoft/pyright#3439.