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

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

import pytest
from fastapi.exceptions import FastAPIError
from fastapi.testclient import TestClient


@pytest.fixture(name="client")
def get_client():
    from docs_src.dependencies.tutorial008c_an import app

    client = TestClient(app)
    return client


def test_get_no_item(client: TestClient):
    response = client.get("/items/foo")
    assert response.status_code == 404, response.text

import pytest
from fastapi.testclient import TestClient

from docs_src.path_operation_configuration.tutorial006 import app

client = TestClient(app)


@pytest.mark.parametrize(
    "path,expected_status,expected_response",
    [
        ("/items/", 200, [{"name": "Foo", "price": 42}]),
        ("/users/", 200, [{"username": "johndoe"}]),
        ("/elements/", 200, [{"item_id": "Foo"}]),
    ],
)

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.

# Corpo - Modelos aninhados

Com o **FastAPI**, você pode definir, validar, documentar e usar modelos profundamente aninhados de forma arbitrária (graças ao Pydantic).

## Campos do tipo Lista

Você pode definir um atributo como um subtipo. Por exemplo, uma `list` do Python:

```Python hl_lines="14"
{!../../docs_src/body_nested_models/tutorial001.py!}
```

from fastapi.testclient import TestClient

from docs_src.response_cookies.tutorial001 import app

client = TestClient(app)


def test_path_operation():
    response = client.post("/cookie/")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Come to the dark side, we have cookies"}

from fastapi.testclient import TestClient

from docs_src.response_cookies.tutorial002 import app

client = TestClient(app)


def test_path_operation():
    response = client.post("/cookie-and-object/")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Come to the dark side, we have cookies"}

def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/": {
                "get": {
                    "responses": {
                        "200": {
                            "description": "Successful Response",