Ability to define response_model with native typing

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn’t find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google “How to X in FastAPI” and didn’t find any information.
• I already read and followed all the tutorial in the docs and didn’t find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from fastapi import FastAPI

from pydantic import BaseModel

app = FastAPI()


class TypicalResponse(BaseModel):
    msg: str
    data: int


@app.get("/add/{x}/{y}")
async def add(x: int, y: int) -> TypicalResponse:
    return TypicalResponse(msg="Done!", data=x + y)

Description

Open the automatic doc on this handler See no output schema defined I would like to use typing “-> Type” for annotate response model. This is good for simple handlers.

Wanted Solution

I would like to autodoc parse this typing same as “response_model=TypicalResponse”

Wanted Code

from fastapi import FastAPI

from pydantic import BaseModel

app = FastAPI()

# Same
class TypicalResponse(BaseModel):
    msg: str
    data: int


@app.get("/add/{x}/{y}")
async def add(x: int, y: int) -> TypicalResponse:
    return TypicalResponse(msg="Done!", data=x + y)

Alternatives

I use kwarg “response_model” as single alternative But typing already defines the output model, necessary duplicate as result.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.79.0

Python Version

Python 3.9.0

Additional Context

Without patch:

With patch:

I think second is better by avoid information duplication

Meanwhile, solution is quite simple. One of the ways to implement (don’t judge too much, that’s first idea):

1. Open APIRouter class
2. Modify self.add_api_route by adding

May be dirty, so welcome to search another ways.

[chbndrhnns]

This idea has been rejected previously: https://github.com/tiangolo/fastapi/issues/101

[AbstractiveNord]

Essential… Well, i mean it’s because this functionality expected to be as basic (by any newbie at least). FastAPI have Pydantic native intergration, very pythonic style, you may think “wow, nice framework!” And boom! - This typing isn’t working. Not critical, but still.

Exactly - I literally went through this! Would be great if we can somehow make this work. If this indeed breaks something, can this configuration be used as an input for those who wants to go use the return types instead of duplicating it in reponse_model?

My patch is very soft.It checks response_model to be None before grabbing model from annotations.I can agree with problems, mypy, everything, but for newbies it’s great, meanwhile everyone can directly set response_model and my patch will not do a thing.

Welcome to test