```Python
with open("file.txt") as file:
    file.read()
```

Em versões mais recentes do Python, há também um **gerenciador de contexto assíncrono**. Você o usaria com `async with`:

```Python
async with lifespan(app):
    await do_stuff()
```

`UploadFile` 有以下 `async` 方法。它們底層會呼叫對應的檔案方法（使用內部的 `SpooledTemporaryFile`）。

* `write(data)`：將 `data` (`str` 或 `bytes`) 寫入檔案。
* `read(size)`：讀取檔案的 `size` (`int`) 個位元組/字元。
* `seek(offset)`：移動到檔案中的位元組位置 `offset` (`int`)。
    * 例如，`await myfile.seek(0)` 會移到檔案開頭。
    * 當你已經執行過 `await myfile.read()`，之後需要再次讀取內容時特別有用。
* `close()`：關閉檔案。

由於這些都是 `async` 方法，你需要以 await 呼叫它們。

例如，在 `async` 的路徑操作函式中可這樣讀取內容：

from typing import Annotated

from fastapi import FastAPI, File, UploadFile

app = FastAPI()


@app.post("/files/")
async def create_file(file: Annotated[bytes, File()]):
    return {"file_size": len(file)}


@app.post("/uploadfile/")
async def create_upload_file(file: UploadFile):

app = FastAPI()


@app.exception_handler(StarletteHTTPException)
async def http_exception_handler(request, exc):
    return PlainTextResponse(str(exc.detail), status_code=exc.status_code)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc: RequestValidationError):
    message = "Validation errors:"
    for error in exc.errors():

app = FastAPI()


@app.exception_handler(StarletteHTTPException)
async def custom_http_exception_handler(request, exc):
    print(f"OMG! An HTTP error!: {repr(exc)}")
    return await http_exception_handler(request, exc)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
    print(f"OMG! The client sent invalid data!: {exc}")

from typing import Annotated

from fastapi import Header, HTTPException


async def get_token_header(x_token: Annotated[str, Header()]):
    if x_token != "fake-super-secret-token":
        raise HTTPException(status_code=400, detail="X-Token header invalid")


async def get_query_token(token: str):
    if token != "jessica":

## Utiliser `async` ou non { #to-async-or-not-to-async }

Comme les dépendances seront aussi appelées par **FastAPI** (tout comme vos fonctions de chemins d’accès), les mêmes règles s’appliquent lors de la définition de vos fonctions.

Vous pouvez utiliser `async def` ou un `def` normal.

        {"detail": exc.detail}, status_code=exc.status_code, headers=headers
    )


async def request_validation_exception_handler(
    request: Request, exc: RequestValidationError
) -> JSONResponse:
    return JSONResponse(
        status_code=422,
        content={"detail": jsonable_encoder(exc.errors())},
    )


async def websocket_request_validation_exception_handler(

from fastapi.responses import HTMLResponse

app = FastAPI()


@app.post("/files/")
async def create_files(
    files: list[bytes] = File(description="Multiple files as bytes"),
):
    return {"file_sizes": [len(file) for file in files]}


@app.post("/uploadfiles/")
async def create_upload_files(
    files: list[UploadFile] = File(description="Multiple files as UploadFile"),
):

from fastapi import FastAPI, Security
from fastapi.security import SecurityScopes
from fastapi.testclient import TestClient


async def security1(scopes: SecurityScopes):
    return scopes.scopes


async def security2(scopes: SecurityScopes):
    return scopes.scopes


async def dep3(
    dep1: Annotated[list[str], Security(security1, scopes=["scope1"])],