Issues with custom decorators

[ThirumalaiK]

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Example Code

main.py

from __future__ import annotations

from functools import wraps

from fastapi import FastAPI, Request, Response

from auth import auth_external

app = FastAPI()


def auth_internal(fn):
    @wraps(fn)
    async def async_wrapper(*args, **kwargs):
        return await fn(*args, **kwargs)

    return async_wrapper


@app.get("/{_:path}")
@auth_external
async def route1(_: Request):
    return Response(status_code=204)

auth.py

from __future__ import annotations

from functools import wraps


def auth_external(fn):
    @wraps(fn)
    async def async_wrapper(*args, **kwargs):
        return await fn(*args, **kwargs)

    return async_wrapper

Description

I've experienced weird behaviour with decorators from defined on other modules.

Getting pydantic.errors.PydanticUndefinedAnnotation: name 'Request' is not defined on using a decorator defined on other modules (i.e. auth.auth_external). But, the same works when the decorator copied to the main module (i.e auth_internal)

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.109.2

Pydantic Version

2.6.1

Python Version

Python 3.10.12

Additional Context

No response

[YuriiMotov]

Can confirm that behavior.
But everything works fine if you either remove from __future__ import annotations from main.py or add from fastapi import Request to auth.py

[pfan94]

@wraps(fn, updated=("__dict__", "__globals__")) worked for me

[ghost]

This is a good fix. However, in some cases, you cannot change the decorator's behavior (e.g. a third-party library). This is how we worked around it: #12496

I'll see if your fix is applicable in our case, as that would be preferable

[YuriiMotov]

Try using this approach:

from __future__ import annotations

from functools import wraps
from typing import get_type_hints

from fastapi import FastAPI, Request, Response

from auth import auth_external

app = FastAPI()

def evaluate_annotations(fn):
    fn.__annotations__ = get_type_hints(fn)
    return fn


@app.get("/internal/{_:path}")
@auth_internal
async def route_internal(_: Request):
    return Response(status_code=204)


@app.get("/external/{_:path}")
@auth_external
@evaluate_annotations
async def route_external(_: Request):
    return Response(status_code=204)

When __future__.annotations is imported, it forces Python to store annotations as strings in runtime. And this brakes the logic.
So, I added evaluate_annotations decorator that just evaluates annotations

[YuriiMotov]

This was fixed by #5077, works well with FastAPI 0.123.5+