따라서 아래의 함수는 인자 조합마다 한 번씩 실행됩니다. 그리고 각각의 인자 조합에 대해 반환된 값은, 함수가 정확히 같은 인자 조합으로 호출될 때마다 반복해서 사용됩니다.

예를 들어 다음 함수가 있다면:

```Python
@lru_cache
def say_hi(name: str, salutation: str = "Ms."):
    return f"Hello {salutation} {name}"
```

프로그램은 다음과 같이 실행될 수 있습니다:

```mermaid
sequenceDiagram

participant code as Code
participant function as say_hi()

app = FastAPI()


def get_username():
    try:
        yield "Rick"
    finally:
        print("Cleanup up before response is sent")


@app.get("/users/me")
def get_user_me(username: str = Depends(get_username, scope="function")):

from fastapi import FastAPI, File, Form, UploadFile

app = FastAPI()


@app.post("/files/")
async def create_file(
    file: Annotated[bytes, File()],
    fileb: Annotated[UploadFile, File()],
    token: Annotated[str, Form()],
):
    return {
        "file_size": len(file),
        "token": token,
        "fileb_content_type": fileb.content_type,

### Create an `Enum` class { #create-an-enum-class }

Import `Enum` and create a sub-class that inherits from `str` and from `Enum`.

By inheriting from `str` the API docs will be able to know that the values must be of type `string` and will be able to render correctly.

Then create class attributes with fixed values, which will be the available valid values:

media_type = "application/vnd.api+json"


# NOTE: These are not valid JSON:API resources
# but they are fine for testing requestBody with custom media_type
class Product(BaseModel):
    name: str
    price: float


class Shop(BaseModel):
    name: str


@app.post("/products")
async def create_product(data: Product = Body(media_type=media_type, embed=True)):
    pass  # pragma: no cover


@app.post("/shops")

///

## 它做了什麼 { #what-it-does }

它會從請求中尋找 `Authorization` 標頭，檢查其值是否為 `Bearer ` 加上一段 token，並將該 token 以 `str` 回傳。

若未找到 `Authorization` 標頭，或其值不是 `Bearer ` token，則會直接回傳 401（`UNAUTHORIZED`）錯誤。

你不必再自行檢查 token 是否存在；你可以確信只要你的函式被執行，該 token 參數就一定會是 `str`。

你可以在互動式文件中試試看：

<img src="/img/tutorial/security/image03.png">

我們還沒驗證 token 是否有效，但這已是個開始。

## 小結 { #recap }

///

## 它做了什么 { #what-it-does }

它会在请求中查找 `Authorization` 请求头，检查其值是否为 `Bearer ` 加上一些令牌，并将该令牌作为 `str` 返回。

如果没有 `Authorization` 请求头，或者其值不包含 `Bearer ` 令牌，它会直接返回 401 状态码错误（`UNAUTHORIZED`）。

你甚至无需检查令牌是否存在即可返回错误；只要你的函数被执行，就可以确定会拿到一个 `str` 类型的令牌。

你已经可以在交互式文档中试试了：

<img src="/img/tutorial/security/image03.png">

我们还没有验证令牌是否有效，但这已经是一个良好的开端。

## 小结 { #recap }

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str | None, Query(min_length=3)]):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

async def add_process_time_header(request: Request, call_next):
    start_time = time.perf_counter()
    response = await call_next(request)
    process_time = time.perf_counter() - start_time
    response.headers["X-Process-Time"] = str(process_time)

from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool | None = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")