pydantic validation PyCharm: This decorator will not receive a callable it may expect; the built-in decorator returns a special object

Question

from pydantic import BaseModel


class Request(BaseModel):
    num: int

    @validator("num")
    @classmethod
    def validate_num(cls, num: int) -> int:
        return num

PyCharm gives the warning "This decorator will not receive a callable it may expect; the built-in decorator returns a special object" for the above code. I don't think the warning is clear so I'd appreciate some help.

When I change the above code to this:

from fastapi.exceptions import RequestValidationError

from pydantic import BaseModel, validator
from pydantic.error_wrappers import ErrorWrapper


class Request(BaseModel):
    num: int

    @classmethod
    @validator("num")
    def validate_num(cls, num: int) -> int:
        if num < 0:
            raise RequestValidationError([ErrorWrapper(ValueError("error"), ())])
        return num


request = Request(num=-2)

The warning goes away, but the code executes without any problem when it's not supposed to, meaning that the validation has been ignored for some reason.

Answer 1

Looking at the source code on github, you'll see that the validator decorator already returns a classmethod.

def validator(
    *fields: str,
    mode: Literal['before', 'after', 'wrap', 'plain'] = 'after',
    check_fields: bool | None = None,
    sub_path: tuple[str | int, ...] | None = None,
    allow_reuse: bool = False,
) -> Callable[[Callable[..., Any]], classmethod[Any]]:

Simply remove your @classmethod decorator!

Answer 2

Your code is correct

It's false positive hint in PyCharm

Related issue: https://youtrack.jetbrains.com/issue/PY-34368/False-warning-This-decorator-will-not-receive-a-callable-it-may-expect-when-classmethod-is-not-the-last-applied

Workaround

Add this string above decorators:

# noinspection PyNestedDecorators