**FastAPI** は、それぞれの場合の処理​​方法と同じオブジェクトの再利用方法を知っているため、すべてのバックグラウンドタスクがマージされ、バックグラウンドで後で実行されます。

```Python hl_lines="13  15  22  25"
{!../../../docs_src/background_tasks/tutorial002.py!}
```

この例では、レスポンスが送信された *後* にメッセージが `log.txt` ファイルに書き込まれます。

リクエストにクエリがあった場合、バックグラウンドタスクでログに書き込まれます。

そして、*path operations 関数* で生成された別のバックグラウンドタスクは、`email` パスパラメータを使用してメッセージを書き込みます。

## 技術的な詳細

    {!> ../../../docs_src/background_tasks/tutorial002.py!}
    ```

In obigem Beispiel werden die Nachrichten, *nachdem* die Response gesendet wurde, in die Datei `log.txt` geschrieben.

Wenn im Request ein Query-Parameter enthalten war, wird dieser in einem Hintergrundtask in das Log geschrieben.

Und dann schreibt ein weiterer Hintergrundtask, der in der *Pfadoperation-Funktion* erstellt wird, eine Nachricht unter Verwendung des Pfad-Parameters `email`.

Do you want to just have a `str`? Or just a `dict`? Or a database class model instance directly? It all works the same way.

You actually don't have users that log in to your application but robots, bots, or other systems, that have just an access token? Again, it all works the same.

from typing_extensions import Annotated

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: Union[str, None] = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q


@app.post("/send-notification/{email}")

```Python hl_lines="6"
{!../../../docs_src/events/tutorial002.py!}
```

Hier schreibt die `shutdown`-Eventhandler-Funktion eine Textzeile `"Application shutdown"` in eine Datei `log.txt`.

!!! info
    In der Funktion `open()` bedeutet `mode="a"` „append“ („anhängen“), sodass die Zeile nach dem, was sich in dieser Datei befindet, hinzugefügt wird, ohne den vorherigen Inhalt zu überschreiben.

```Python hl_lines="6"
{!../../../docs_src/events/tutorial002.py!}
```

Aqui, a função de manipulação de evento `shutdown` irá escrever uma linha de texto `"Application shutdown"` no arquivo `log.txt`.

!!! info "Informação"
    Na função `open()`, o `mode="a"` significa "acrescentar", então, a linha irá ser adicionada depois de qualquer coisa que esteja naquele arquivo, sem sobrescrever o conteúdo anterior.

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: Union[str, None] = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q


@app.post("/send-notification/{email}")

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: str | None = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q


@app.post("/send-notification/{email}")

    client = TestClient(app)
    log = Path("log.txt")
    if log.is_file():
        os.remove(log)  # pragma: no cover
    response = client.post("/send-notification/******@****.***?q=some-query")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Message sent"}
    with open("./log.txt") as f:

    client = TestClient(app)
    log = Path("log.txt")
    if log.is_file():
        os.remove(log)  # pragma: no cover
    response = client.post("/send-notification/******@****.***?q=some-query")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Message sent"}
    with open("./log.txt") as f: