## 响应模型编码参数

你的响应模型可以具有默认值，例如：

```Python hl_lines="11  13-14"
{!../../docs_src/response_model/tutorial004.py!}
```

* `description: Union[str, None] = None` 具有默认值 `None`。
* `tax: float = 10.5` 具有默认值 `10.5`.
* `tags: List[str] = []` 具有一个空列表作为默认值： `[]`.

但如果它们并没有存储实际的值，你可能想从结果中忽略它们的默认值。

举个例子，当你在 NoSQL 数据库中保存了具有许多可选属性的模型，但你又不想发送充满默认值的很长的 JSON 响应。

    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_py310
def test_override_in_users_with_q():
    from docs_src.dependency_testing.tutorial001_py310 import client

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

    rules:
      - apiGroups:
          - ""
        apiVersions:
          - v1
        operations:
          - CREATE
        resources:
          - pods
        scope: '*'
    sideEffects: None
    timeoutSeconds: 10
  - admissionReviewVersions:
      - v1beta1
      - v1
    clientConfig:
      service:
        name: istiod-1-16
        namespace: istio-system
        path: /inject

    assertEquals(0, queue.size());
    assertEquals(3, queue.remainingCapacity());

    assertTrue(queue.add("one"));
    assertTrue(queue.add("two"));
    assertTrue(queue.add("three"));
    assertEquals("one", queue.element());
    assertEquals("one", queue.peek());
    assertEquals(3, queue.size());
    assertEquals(0, queue.remainingCapacity());

    assertTrue(queue.add("four"));

	}

	opts := madmin.DriveSpeedTestOpts{
		Serial:    serial,
		BlockSize: blockSize,
		FileSize:  fileSize,
	}

	done := keepHTTPResponseAlive(w)
	result := driveSpeedTest(r.Context(), opts)
	done(nil)

	peersLogIf(r.Context(), gob.NewEncoder(w).Encode(result))
}

// GetReplicationMRFHandler - returns replication MRF for bucket

echo "done"

if [ ! -f ./mc ]; then
	echo -n "Downloading MinIO client ..."
	wget -O mc https://dl.min.io/client/mc/release/linux-amd64/mc &&
		chmod +x mc
	echo "done"
fi

export MC_HOST_minio1=https://minio:minio123@localhost:9001
export MC_HOST_minio2=https://minio:minio123@localhost:9002

/**
 * A {@link FutureTask} that also implements the {@link ListenableFuture} interface. Unlike {@code
 * FutureTask}, {@code ListenableFutureTask} does not provide an overrideable {@link
 * FutureTask#done() done()} method. For similar functionality, call {@link #addListener}.
 *
 * <p>Few users should use this class. It is intended primarily for those who are implementing an

`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!}
```

func (x *XDGSCRAMClient) Step(challenge string) (response string, err error) {
	response, err = x.ClientConversation.Step(challenge)
	return
}

// Done returns true if the conversation is completed or has errored.
func (x *XDGSCRAMClient) Done() bool {
	return x.ClientConversation.Done()

Deleting the cache when it is no longer needed can be done.  However this may delete the purpose of the cache
which is designed to persist between app restarts.

```kotlin
cache.delete()
```
 
## Pruning the Cache

Pruning the entire Cache to clear space temporarily can be done using evictAll.

```kotlin
cache.evictAll()
```

Removing individual items can be done using the urls iterator.