⤴️ 👥 💪 ✍ `AsyncClient` ⏮️ 📱, & 📨 🔁 📨 ⚫️, ⚙️ `await`.

```Python hl_lines="9-10"
{!../../../docs_src/async_tests/test_main.py!}
```

👉 🌓:

```Python
response = client.get('/')
```

...👈 👥 ⚙️ ⚒ 👆 📨 ⏮️ `TestClient`.

!!! tip
    🗒 👈 👥 ⚙️ 🔁/⌛ ⏮️ 🆕 `AsyncClient` - 📨 🔁.

## 🎏 🔁 🔢 🤙

    legacy_request_state_context_var.reset(contextvar_token)


@app.middleware("http")
async def custom_middleware(
    request: Request, call_next: Callable[[Request], Awaitable[Response]]
):
    response = await call_next(request)
    response.headers["custom"] = "foo"
    return response


@app.get("/user", dependencies=[Depends(set_up_request_state_dependency)])
def get_user():

## Nachrichten erwarten und Nachrichten senden

In Ihrer WebSocket-Route können Sie Nachrichten `await`en und Nachrichten senden.

```Python hl_lines="48-52"
{!../../../docs_src/websockets/tutorial001.py!}
```

Sie können Binär-, Text- und JSON-Daten empfangen und senden.

## Es ausprobieren

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

In neueren Versionen von Python gibt es auch einen **asynchronen Kontextmanager**. Sie würden ihn mit `async with` verwenden:

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

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

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

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

Nesse caso, a função de tarefa gravará em um arquivo (simulando o envio de um e-mail).

E como a operação de gravação não usa `async` e `await`, definimos a função com `def` normal:

```Python hl_lines="6-9"
{!../../../docs_src/background_tasks/tutorial001.py!}
```

## Adicionar a tarefa em segundo plano

In diesem Fall schreibt die Taskfunktion in eine Datei (den Versand einer E-Mail simulierend).

Und da der Schreibvorgang nicht `async` und `await` verwendet, definieren wir die Funktion mit normalem `def`:

```Python hl_lines="6-9"
{!../../../docs_src/background_tasks/tutorial001.py!}
```

## Den Hintergrundtask hinzufügen

As our code is calling Couchbase and we are not using the <a href="https://docs.couchbase.com/python-sdk/2.5/async-programming.html#asyncio-python-3-5" class="external-link" target="_blank">experimental Python <code>await</code> support</a>, we should declare our function with normal `def` instead of `async def`.

def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>Vagy használd az <code>async def</code>-et...</summary>

Ha a kódod `async` / `await`-et, használ `async def`:

```Python hl_lines="9  14"
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def read_root():

def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>O usa <code>async def</code>...</summary>

Si tu código usa `async` / `await`, usa `async def`:

```Python hl_lines="7  12"
from fastapi import FastAPI
from typing import Union

app = FastAPI()


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