from fastapi import APIRouter, Body

router = APIRouter()


@router.post("/compute")
def compute(a: int = Body(), b: str = Body()):

If you are working with **FastAPI** you don't have to worry about that, because that "first" function will be your *path operation function*, and FastAPI will know how to do the right thing.

But if you want to use `async` / `await` without FastAPI, you can do it as well.

### Write your own async code

# Middleware

Sie können Middleware zu **FastAPI**-Anwendungen hinzufügen.

Eine „Middleware“ ist eine Funktion, die mit jedem **Request** arbeitet, bevor er von einer bestimmten *Pfadoperation* verarbeitet wird. Und auch mit jeder **Response**, bevor sie zurückgegeben wird.

* Sie nimmt jeden **Request** entgegen, der an Ihre Anwendung gesendet wird.
* Sie kann dann etwas mit diesem **Request** tun oder beliebigen Code ausführen.

import importlib

import pytest
from dirty_equals import IsDict
from fastapi.testclient import TestClient
from inline_snapshot import snapshot

from tests.utils import needs_py39, needs_py310, needs_pydanticv1, needs_pydanticv2


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002", marks=needs_pydanticv2),
        pytest.param("tutorial002_py310", marks=[needs_py310, needs_pydanticv2]),

from dirty_equals import IsDict
from fastapi.testclient import TestClient

from docs_src.request_files.tutorial002 import app

client = TestClient(app)


def test_post_form_no_body():
    response = client.post("/files/")
    assert response.status_code == 422, response.text
    assert response.json() == IsDict(
        {
            "detail": [
                {
                    "type": "missing",

To do that, we declare a method `__call__`:

{* ../../docs_src/dependencies/tutorial011_an_py39.py hl[12] *}

In this case, this `__call__` is what **FastAPI** will use to check for additional parameters and sub-dependencies, and this is what will be called to pass a value to the parameter in your *path operation function* later.

## Parameterize the instance

from fastapi.testclient import TestClient

from docs_src.custom_response.tutorial009c import app

client = TestClient(app)


def test_get():
    response = client.get("/")

from fastapi.testclient import TestClient

from docs_src.custom_response.tutorial007 import app

client = TestClient(app)


def test_get():
    fake_content = b"some fake video bytes"
    response = client.get("/")

github_graphql_url = "https://api.github.com/graphql"
questions_translations_category_id = "DIC_kwDOCZduT84CT5P9"

all_discussions_query = """
query Q($category_id: ID) {
  repository(name: "fastapi", owner: "fastapi") {
    discussions(categoryId: $category_id, first: 100) {
      nodes {
        title
        id
        number
        labels(first: 10) {
          edges {
            node {
              id

따라서 모든 작업을 의도한대로 실행하기 위해, 허용되는 출처를 명시적으로 지정하는 것이 좋습니다.

## `CORSMiddleware` 사용

`CORSMiddleware` 을 사용하여 **FastAPI** 응용 프로그램의 교차 출처 리소스 공유 환경을 설정할 수 있습니다.

* `CORSMiddleware` 임포트.
* 허용되는 출처(문자열 형식)의 리스트 생성.
* FastAPI 응용 프로그램에 "미들웨어(middleware)"로 추가.

백엔드에서 다음의 사항을 허용할지에 대해 설정할 수도 있습니다:

* 자격증명 (인증 헤더, 쿠키 등).
* 특정한 HTTP 메소드(`POST`, `PUT`) 또는 와일드카드 `"*"` 를 사용한 모든 HTTP 메소드.