在這種情況下（未使用 `Annotated`），我們必須用 `Query()` 取代函式中的預設值 `None`，因此需要用 `Query(default=None)` 來設定預設值；對 FastAPI 而言，這達到相同目的。

所以：

```Python
q: str | None = Query(default=None)
```

…會讓參數變為可選、預設值是 `None`，等同於：

```Python
q: str | None = None
```

但用 `Query` 的版本會明確宣告它是查詢參數。

接著，我們可以傳更多參數給 `Query`。此例中是用於字串的 `max_length` 參數：

```Python
q: str | None = Query(default=None, max_length=50)
```

app = FastAPI()


@app.post("/urlencoded")
async def post_url_encoded(age: Annotated[int | None, Form()] = None):
    return age


@app.post("/multipart")
async def post_multi_part(
    age: Annotated[int | None, Form()] = None,
    file: Annotated[bytes | None, File()] = None,
):
    return {"file": file, "age": age}


client = TestClient(app)


def test_form_default_url_encoded():

```Python
say_hi(name=None)  # Das funktioniert, None ist gültig 🎉
```

Die gute Nachricht ist: In den meisten Fällen können Sie einfach `|` verwenden, um Unions von Typen zu definieren:

```python
def say_hi(name: str | None):
    print(f"Hey {name}!")
```

```Python
say_hi(name=None)  # Ceci fonctionne, None est valide 🎉
```

La bonne nouvelle, c'est que, dans la plupart des cas, vous pourrez simplement utiliser `|` pour définir des unions de types :

```python
def say_hi(name: str | None):
    print(f"Hey {name}!")
```

            "price": 50.5,
            "description": None,
            "tax": None,
        },
        "user": {"username": "Dave", "full_name": None},
    }


def test_put_missing_body(client: TestClient):
    response = client.put("/items/5")
    assert response.status_code == 422
    assert response.json() == {
        "detail": [
            {
                "input": None,
                "loc": [

Пришло время использовать его с FastAPI. 🚀

У нас была такая аннотация типа:

```Python
q: str | None = None
```

Мы «обернём» это в `Annotated`, и получится:

```Python
q: Annotated[str | None] = None
```

Обе версии означают одно и то же: `q` — параметр, который может быть `str` или `None`, и по умолчанию равен `None`.

А теперь к самому интересному. 🎉

// It returns the byte index in s of the first Unicode
// code point satisfying f(c), or -1 if none do.
func IndexFunc(s []byte, f func(r rune) bool) int {
	return indexFunc(s, f, true)
}

// LastIndexFunc interprets s as a sequence of UTF-8-encoded code points.
// It returns the byte index in s of the last Unicode
// code point satisfying f(c), or -1 if none do.
func LastIndexFunc(s []byte, f func(r rune) bool) int {

Wir hatten diese Typannotation:

```Python
q: str | None = None
```

Was wir tun werden, ist, dies mit `Annotated` zu wrappen, sodass es zu:

```Python
q: Annotated[str | None] = None
```

Beide dieser Versionen bedeuten dasselbe: `q` ist ein Parameter, der ein `str` oder `None` sein kann, und standardmäßig ist er `None`.

Jetzt springen wir zu den spannenden Dingen. 🎉

Agora é a hora de usá-lo com FastAPI. 🚀

Tínhamos esta anotação de tipo:

```Python
q: str | None = None
```

O que faremos é envolver isso com `Annotated`, para que fique assim:

```Python
q: Annotated[str | None] = None
```

Ambas as versões significam a mesma coisa, `q` é um parâmetro que pode ser `str` ou `None`, e por padrão é `None`.

Agora vamos pular para a parte divertida. 🎉

async def override_dependency(q: str | None = None):
    return {"q": q, "skip": 5, "limit": 10}


app.dependency_overrides[common_parameters] = override_dependency


def test_override_in_items():
    response = client.get("/items/")
    assert response.status_code == 200
    assert response.json() == {
        "message": "Hello Items!",
        "params": {"q": None, "skip": 5, "limit": 10},
    }