The first thing to notice, is that we are defining an async function with `yield`. This is very similar to Dependencies with `yield`.

{* ../../docs_src/events/tutorial003_py310.py hl[14:19] *}

The first part of the function, before the `yield`, will be executed **before** the application starts.

And the part after the `yield` will be executed **after** the application has finished.

### Async Context Manager { #async-context-manager }

在這個範例中因為是存在記憶體的假檔案（`io.BytesIO`），影響不大；但若是實際檔案，務必在處理完成後關閉檔案。

### 檔案與 Async { #files-and-async }

多數情況下，類檔案物件預設不相容於 async/await。

例如，它們沒有 `await file.read()`，也不支援 `async for chunk in file`。

而且在許多情況下，讀取它們會是阻塞操作（可能阻塞事件迴圈），因為資料是從磁碟或網路讀取。

/// info

上面的範例其實是例外，因為 `io.BytesIO` 物件已在記憶體中，讀取不會阻塞任何東西。

但在多數情況下，讀取檔案或類檔案物件會造成阻塞。

///

為了避免阻塞事件迴圈，你可以將路徑操作函式宣告為一般的 `def`（而非 `async def`），這樣 FastAPI 會在 threadpool worker 上執行它，避免阻塞主事件迴圈。

]


@app.get("/items/stream")
async def stream_items() -> AsyncIterable[Item]:
    for item in items:
        yield item


@app.get("/items/stream-no-async")
def stream_items_no_async() -> Iterable[Item]:
    for item in items:
        yield item


@app.get("/items/stream-no-annotation")
async def stream_items_no_annotation():
    for item in items:
        yield item

### Файлы и async { #files-and-async }

В большинстве случаев «файлоподобные» объекты по умолчанию не совместимы с async и await.

Например, у них нет `await file.read()` или `async for chunk in file`.

    )


@app.get(app.swagger_ui_oauth2_redirect_url, include_in_schema=False)
async def swagger_ui_redirect():
    return get_swagger_ui_oauth2_redirect_html()


@app.get("/redoc", include_in_schema=False)
async def redoc_html():
    return get_redoc_html(
        openapi_url=app.openapi_url,
        title=app.title + " - ReDoc",

from fastapi.testclient import TestClient

app = FastAPI()


async def common_parameters(q: str | None = None, skip: int = 0, limit: int = 100):
    return {"q": q, "skip": skip, "limit": limit}


@app.get("/items/")
async def read_items(commons: dict = Depends(common_parameters)):
    return {"message": "Hello Items!", "params": commons}


@app.get("/users/")
async def read_users(commons: dict = Depends(common_parameters)):

if TYPE_CHECKING:  # pragma: no cover
    from collections.abc import AsyncGenerator


class DummyClient:
    async def get_people(self) -> list:
        return ["John Doe", "Jane Doe"]

    async def close(self) -> None:
        pass


async def get_client() -> AsyncGenerator[DummyClient, None]:
    client = DummyClient()
    yield client
    await client.close()

            )
    return user


async def get_current_active_user(
    current_user: User = Security(get_current_user, scopes=["me"]),
):
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user


@app.post("/token")
async def login_for_access_token(
    form_data: OAuth2PasswordRequestForm = Depends(),

### Archivos y async { #files-and-async }

En la mayoría de los casos, los objetos tipo archivo no son compatibles con `async` y `await` por defecto.

Por ejemplo, no tienen un `await file.read()`, ni un `async for chunk in file`.

	}

	// Attempt all calls.
	_, err = lkClient.RLock(t.Context(), dsync.LockArgs{})
	if err == nil {
		t.Fatal("Expected for Rlock to fail")
	}

	_, err = lkClient.Lock(t.Context(), dsync.LockArgs{})
	if err == nil {
		t.Fatal("Expected for Lock to fail")
	}

	_, err = lkClient.RUnlock(t.Context(), dsync.LockArgs{})
	if err == nil {
		t.Fatal("Expected for RUnlock to fail")
	}