app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


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


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):

     * Returns the range of this constraint, or {@code null} if none.
     * <p>
     * Note: only one, this method or {@link #getRecommendedVersion()} method must return non-{@code null} value.
     */
    @Nullable
    VersionRange getVersionRange();

    /**
     * Returns the recommended version of this constraint, or {@code null} if none.
     * <p>

`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!}
```

http://127.0.0.1:8000/items/?skip=20
```

🔢 💲 👆 🔢 🔜:

* `skip=20`: ↩️ 👆 ⚒ ⚫️ 📛
* `limit=10`: ↩️ 👈 🔢 💲

## 📦 🔢

🎏 🌌, 👆 💪 📣 📦 🔢 🔢, ⚒ 👫 🔢 `None`:

{* ../../docs_src/query_params/tutorial002.py hl[9] *}

👉 💼, 🔢 🔢 `q` 🔜 📦, & 🔜 `None` 🔢.

/// check

👀 👈 **FastAPI** 🙃 🥃 👀 👈 ➡ 🔢 `item_id` ➡ 🔢 & `q` 🚫,, ⚫️ 🔢 🔢.

///

## 🔢 🔢 🆎 🛠️

You would have **one single `engine` object** for all your code to connect to the same database.

{* ../../docs_src/sql_databases/tutorial001_an_py310.py ln[14:18] hl[14:15,17:18] *}

Using `check_same_thread=False` allows FastAPI to use the same SQLite database in different threads. This is necessary as **one single request** could use **more than one thread** (for example in dependencies).

## Paramètres optionnels

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

{* ../../docs_src/query_params/tutorial002.py hl[9] *}

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

/// check | Remarque

## Parâmetros opcionais

Da mesma forma, você pode declarar parâmetros de consulta opcionais, definindo o valor padrão para `None`:

{* ../../docs_src/query_params/tutorial002_py310.py hl[7] *}

Nesse caso, o parâmetro da função `q` será opcional, e `None` será o padrão.

/// check | Verificar

Tu modelo de response podría tener valores por defecto, como:

{* ../../docs_src/response_model/tutorial004_py310.py hl[9,11:12] *}

* `description: Union[str, None] = None` (o `str | None = None` en Python 3.10) tiene un valor por defecto de `None`.
* `tax: float = 10.5` tiene un valor por defecto de `10.5`.
* `tags: List[str] = []` tiene un valor por defecto de una lista vacía: `[]`.

* `limit=10`: çünkü varsayılan değer buydu.

## İsteğe Bağlı Parametreler

Aynı şekilde, varsayılan değerlerini `None` olarak atayarak isteğe bağlı parametreler tanımlayabilirsiniz:

{* ../../docs_src/query_params/tutorial002_py310.py hl[7] *}

Bu durumda, `q` fonksiyon parametresi isteğe bağlı olacak ve varsayılan değer olarak `None` alacaktır.

/// check | Ek bilgi

        } catch (final UnsupportedEncodingException e) {
            throw new UnsupportedEncodingRuntimeException(e);
        }
    }

    /**
     * Polls an encryption cipher from the queue, creating a new one if none are available.
     *
     * @return an encryption cipher
     */
    protected Cipher pollEncryptoCipher() {
        Cipher cipher = encryptoQueue.poll();
        if (cipher == null) {