Question: Too many arguments for dataclass

Question

• OS: macOS 10.14
• Python version: 3.7.0
• Pydantic version 0.14

---

Hi. I decided to try using pydantic instead of JSON Schemas for validating input / output data in my aiohttp web application, and so far run into strange mypy issue. Let consider next code of adding new project,

from aiohttp import web
from pydantic.dataclasses import dataclass


@dataclass
class AddProject:

    """Add new user project."""

    name: str
    slug: Optional[str]
    description: Optional[str]


@login_required
async def add_project(request: web.Request) -> web.Response:
    """Add new user project."""
    data = AddProject(**await api_request(request))
    user_id = await get_user_id(request)

    async with request.app[APP_DB_KEY].acquire() as conn:
        project = await create_project(
            conn,
            user_id=user_id,
            name=data.name,
            slug=data.slug,
            description=data.description)

    return api_response(project.dict(), status=201)

It works as expected in runtime, but mypy failed with,

error: Too many arguments for "AddProject"

I tried to satisfy mypy by changing AddProject instantiation to,

    raw_data = await api_request(request)
    data = AddProject(
        name=raw_data.get('name'),
        slug=raw_data.get('slug'),
        description=raw_data.get('description'))

but that made mypy failed with,

error: Unexpected keyword argument "name" for "AddProject"
error: Unexpected keyword argument "slug" for "AddProject"
error: Unexpected keyword argument "description" for "AddProject"

I’m a bit curious, as behind that mypy seems to work properly with AddProject, for example, it knows its attributes and fail in case of using missed ones, like data.does_not_exist.

---

Any suggestions on how to make mypy happy? Or this is an expected behaviour, which fixed only by # type: ignore comment?

ps. api_request coroutine returns Dict[Any, Any] if that necessary

[playpauseandstop]

@samuelcolvin

Unfortunately not. It works well with,

from dataclasses import dataclass as py_dataclass


@py_dataclass
class PyAddProject:

    """Add new user project."""

    name: str
    slug: Optional[str]
    description: Optional[str]

mypy succeed, where previously failed with Too many arguments error.

[swannknani]

Enabling mypy plugin fixed the issue for me.