response = client.get("/users/")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "message": "Hello Users!",
        "params": {"q": None, "skip": 5, "limit": 10},
    }


@needs_py39
def test_override_in_users_with_q():
    from docs_src.dependency_testing.tutorial001_an_py39 import client

    response = client.get("/users/?q=foo")

    * Вы можете задать его URL с помощью параметра `docs_url`.
    * Вы можете отключить это с помощью настройки `docs_url=None`.
* **ReDoc**: отображаемый по адресу `/redoc`.
    * Вы можете задать его URL с помощью параметра `redoc_url`.
    * Вы можете отключить это с помощью настройки `redoc_url=None`.

К примеру, чтобы задать отображение Swagger UI по адресу `/documentation` и отключить ReDoc:

```Python hl_lines="3"

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

Because of that, the JSON Schema for a model can be different depending on if it's used for **input or output**:

* for **input** the `description` will **not be required**
* for **output** it will be **required** (and possibly `None`, or in JSON terms, `null`)

</div>

Das bedeutet, dass es **immer einen Wert** hat, der Wert kann jedoch manchmal `None` sein (oder `null` in JSON).

Das bedeutet, dass Clients, die Ihre API verwenden, nicht prüfen müssen, ob der Wert vorhanden ist oder nicht. Sie können davon ausgehen, dass das Feld immer vorhanden ist. In einigen Fällen hat es jedoch nur den Defaultwert `None`.

## Paramètres optionnels

De la même façon, vous pouvez définir des paramètres de requête comme optionnels, en leur donnant comme valeur par défaut `None` :

```Python hl_lines="9"
{!../../docs_src/query_params/tutorial002.py!}
```

Ici, le paramètre `q` sera optionnel, et aura `None` comme valeur par défaut.

/// check | "Remarque"

                    "loc": ["header", "x-token"],
                    "msg": "Field required",
                    "input": None,
                },
                {
                    "type": "missing",
                    "loc": ["header", "x-key"],
                    "msg": "Field required",
                    "input": None,
                },
            ]
        }
    ) | IsDict(
        # TODO: remove when deprecating Pydantic v1

        "lib/gcc/arm-rpi-linux-gnueabihf/**",
        "include/**",
    ]),
)

filegroup(
    name = "aarch64_compiler_pieces",
    srcs = glob([
        "aarch64-none-linux-gnu/**",
        "libexec/**",
        "lib/gcc/aarch64-none-linux-gnu/**",
        "include/**",
    ]),
)

filegroup(
    name = "compiler_components",
    srcs = [
        ":ar",
        ":as",
        ":gcc",

        "name": "Baz",
        "description": None,
        "price": 50.2,
        "tax": 10.5,
        "tags": [],
    }


def test_put(client: TestClient):
    response = client.put(
        "/items/bar", json={"name": "Barz", "price": 3, "description": None}
    )
    assert response.json() == {
        "name": "Barz",
        "description": None,
        "price": 3,
        "tax": 10.5,

        "name": "Baz",
        "description": None,
        "price": 50.2,
        "tax": 10.5,
        "tags": [],
    }


@needs_py310
def test_put(client: TestClient):
    response = client.put(
        "/items/bar", json={"name": "Barz", "price": 3, "description": None}
    )
    assert response.json() == {
        "name": "Barz",
        "description": None,
        "price": 3,
        "tax": 10.5,

`Optional[Something]` là một cách viết ngắn gọn của `Union[Something, None]`, chúng là tương đương nhau.

Điều này cũng có nghĩa là trong Python 3.10, bạn có thể sử dụng `Something | None`:

//// tab | Python 3.10+

```Python hl_lines="1"
{!> ../../docs_src/python_types/tutorial009_py310.py!}
```