## 선택적 매개변수

같은 방법으로 기본값을 `None`으로 설정하여 선택적 매개변수를 선언할 수 있습니다:

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

이 경우 함수 매개변수 `q`는 선택적이며 기본값으로 `None` 값이 됩니다.

/// check | 확인

**FastAPI**는 `item_id`가 경로 매개변수이고 `q`는 경로 매개변수가 아닌 쿼리 매개변수라는 것을 알 정도로 충분히 똑똑합니다.

///

/// note | 참고

FastAPI는 `q`가 `= None`이므로 선택적이라는 것을 인지합니다.

     * <p>
     * This implementation maintains UTC time to ensure monotonic behavior.
     * The provided zone parameter is ignored.
     *
     * @param zone the target timezone (ignored)
     * @return this clock instance
     */
    @Override
    public Clock withZone(ZoneId zone) {
        // Monotonic clock is always UTC-based
        return this;
    }

{!> ../../docs_src/python_types/tutorial008b.py!}
```

////

In both cases this means that `item` could be an `int` or a `str`.

#### Possibly `None` { #possibly-none }

You can declare that a value could have a type, like `str`, but that it could also be `None`.

In Python 3.6 and above (including Python 3.10) you can declare it by importing and using `Optional` from the `typing` module.

```Python hl_lines="1  4"

 */
@Experimental
@Immutable
public enum DependencyScope {

    /**
     * None. Allows you to declare dependencies (for example to alter reactor build order) but in reality dependencies
     * in this scope are not part of any path scope.
     */
    NONE("none", false),

    /**
     * Undefined. When no scope is explicitly given, UNDEFINED will be used, but its meaning will depend on

## Optionale Parameter

Auf die gleiche Weise können Sie optionale Query-Parameter deklarieren, indem Sie deren Defaultwert auf `None` setzen:

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

In diesem Fall wird der Funktionsparameter `q` optional, und standardmäßig `None` sein.

/// check

///

### Flask REST framework'leri

Pek çok Flask REST framework'ü var, fakat bunları biraz araştırdıktan sonra pek çoğunun artık geliştirilmediğini ve göze batan bazı sorunlarının olduğunu gördüm.

### <a href="https://marshmallow.readthedocs.io/en/stable/" class="external-link" target="_blank">Marshmallow</a>

(prefers-reduced-motion: reduce) {\n  .btn {\n    transition: none;\n  }\n}\n\n.btn:hover {\n  color: #212529;\n  text-decoration: none;\n}\n\n.btn:focus, .btn.focus {\n  outline: 0;\n  box-shadow: none;\n}\n\n.btn.disabled, .btn:disabled {\n  opacity: 0.65;\n  box-shadow: none;\n}\n\n.btn:not(:disabled):not(.disabled) {\n  cursor: pointer;\n}\n\n.btn:not(:disabled):not(.disabled):active, .btn:not(:disabled):not(.disabled).active {\n  box-shadow: none;\n}\n\na.btn.disabled,\nfieldset:disabled a.btn {\n  pointer-events:...

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):

     * Verifies that the method returns the correct time zone offset.
     * @throws CIFSException
     */
    @Test
    void testGetServerTimeZoneOffset() throws CIFSException {
        when(smbTreeHandle.getServerTimeZoneOffset()).thenReturn(0L);
        assertEquals(0L, smbTreeHandle.getServerTimeZoneOffset(), "Server time zone offset should be 0");

</div>

Esto significa que **siempre tendrá un valor**, solo que a veces el valor podría ser `None` (o `null` en JSON).

Eso significa que, los clientes que usan tu API no tienen que comprobar si el valor existe o no, pueden **asumir que el campo siempre estará allí**, pero solo que en algunos casos tendrá el valor por defecto de `None`.

La forma de describir esto en OpenAPI es marcar ese campo como **requerido**, porque siempre estará allí.