Ahora, veamos cómo puedes usarlo para devolver una respuesta personalizada.

Digamos que quieres devolver una respuesta <a href="https://en.wikipedia.org/wiki/XML" class="external-link" target="_blank">XML</a>.

    client to send the form field `grant_type` with the value `"password"`, which
    is required in the OAuth2 specification (it seems that for no particular reason),
    while for `OAuth2PasswordRequestForm` `grant_type` is optional.

    Read more about it in the

    myapp = make_app(middleware=[Middleware(errorhandler)])
    client = TestClient(myapp)
    with pytest.raises(WebSocketDisconnect) as e:
        with client.websocket_connect("/depends-err/"):
            pass  # pragma: no cover
    assert e.value.code == status.WS_1006_ABNORMAL_CLOSURE
    assert "NotImplementedError" in e.value.reason


def test_depend_err_handler():

## Running on Startup

In most cases, when you create a web API, you want it to be **always running**, uninterrupted, so that your clients can always access it. This is of course, unless you have a specific reason why you want it to run only in certain situations, but most of the time you want it constantly running and **available**.

### In a Remote Server

Aso, when returning several objects, like in `get_users`, we directly call `list`, like in:

```Python
list(models.User.select())
```

                """
            ),
        ],
        reason: Annotated[
            Union[str, None],
            Doc(
                """
                The reason to close the WebSocket connection.

                It is UTF-8-encoded data. The interpretation of the reason is up to the
                application, it is not specified by the WebSocket specification.

## Detalles Técnicos

Las versiones modernas de Python tienen soporte para **"código asíncrono"** usando algo llamado **"coroutines"**, usando la sintaxis **`async` y `await`**.

Veamos esa frase por partes en las secciones siguientes:

* **Código Asíncrono**
* **`async` y `await`**
* **Coroutines**

## Código Asíncrono

from fastapi._compat import PYDANTIC_V2

needs_py39 = pytest.mark.skipif(sys.version_info < (3, 9), reason="requires python3.9+")
needs_py310 = pytest.mark.skipif(
    sys.version_info < (3, 10), reason="requires python3.10+"
)
needs_pydanticv2 = pytest.mark.skipif(not PYDANTIC_V2, reason="requires Pydantic v2")

    )


async def websocket_request_validation_exception_handler(
    websocket: WebSocket, exc: WebSocketRequestValidationError
) -> None:
    await websocket.close(
        code=WS_1008_POLICY_VIOLATION, reason=jsonable_encoder(exc.errors())

So, you can use `user_agent` as you normally would in Python code, instead of needing to capitalize the first letters as `User_Agent` or something similar.

If for some reason you need to disable automatic conversion of underscores to hyphens, set the parameter `convert_underscores` of `Header` to `False`:

=== "Python 3.10+"

    ```Python hl_lines="10"