// Listen - listen on peers.
func (client *peerRESTClient) Listen(ctx context.Context, listenCh chan<- []byte, v url.Values) {
	go func() {
		for {
			client.doListen(ctx, listenCh, v)
			select {
			case <-ctx.Done():
				return
			default:
				// There was error in the REST request, retry after sometime as probably the peer is down.
				time.Sleep(5 * time.Second)
			}
		}
	}()
}

<la:form action="/search" method="get" styleId="searchForm"
	role="search">
	${fe:facetForm()}${fe:geoForm()}
	<header>
		<nav class="navbar navbar-expand-md navbar-dark fixed-top bg-dark d-print-none">
			<div id="content" class="container">
				<la:link styleClass="navbar-brand d-inline-flex" href="/">
					<img src="${fe:url('/images/logo-head.png')}"
						alt="<la:message key="labels.header_brand_name" />"

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    def __dict__(self):
        raise NotImplementedError()


class RoleEnum(Enum):
    admin = "admin"
    normal = "normal"


class ModelWithConfig(BaseModel):
    role: Optional[RoleEnum] = None

    model_config = {"use_enum_values": True}


class ModelWithAlias(BaseModel):
    foo: str = Field(alias="Foo")


class ModelWithDefault(BaseModel):
    foo: str = ...  # type: ignore

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: bool = None


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


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


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

		cachevalue.Opts{ReturnLastGood: true, NoWait: true},
		func(ctx context.Context) (DataUsageInfo, error) {
			if objAPI == nil {
				return DataUsageInfo{}, errServerNotInitialized
			}
			ctx, done := context.WithTimeout(ctx, 2*time.Second)
			defer done()

			return loadDataUsageFromBackend(ctx, objAPI)
		},
	)
}

// GetBucketUsageInfo return bucket usage info for a given bucket

`Optional[Something]` насправді є скороченням для `Union[Something, None]`, вони еквівалентні.

Це також означає, що в Python 3.10 ви можете використовувати `Something | None`:

//// tab | Python 3.8 і вище

```Python hl_lines="1  4"
{!> ../../docs_src/python_types/tutorial009.py!}
```

쿼리 매개변수를 선언할 때와 같이, 모델 어트리뷰트가 기본 값을 가지고 있어도 이는 필수가 아닙니다. 그외에는 필수입니다. 그저 `None`을 사용하여 선택적으로 만들 수 있습니다.

예를 들면, 위의 이 모델은 JSON "`object`" (혹은 파이썬 `dict`)을 다음과 같이 선언합니다:

```JSON
{
    "name": "Foo",
    "description": "선택적인 설명란",
    "price": 45.2,
    "tax": 3.5
}
```

...`description`과 `tax`는 (기본 값이 `None`으로 되어 있어) 선택적이기 때문에, 이 JSON "`object`"는 다음과 같은 상황에서도 유효합니다:

```JSON
{
    "name": "Foo",

    val agentJarNames: List<String>
        get() = agentJars.files.map { it.name }

    @get:InputFiles
    @get:PathSensitive(PathSensitivity.NONE)
    abstract val unixScriptTemplate: ConfigurableFileCollection

    @get:InputFiles
    @get:PathSensitive(PathSensitivity.NONE)
    abstract val windowsScriptTemplate: ConfigurableFileCollection

    @get:OutputDirectory
    abstract val startScriptsDir: DirectoryProperty

                echo "Smokeshow upload success!"
                break
            fi
            echo "Smokeshow upload error, sleep 1 sec and try again."
            sleep 1
          done
        env:
          SMOKESHOW_GITHUB_STATUS_DESCRIPTION: Coverage {coverage-percentage}
          SMOKESHOW_GITHUB_COVERAGE_THRESHOLD: 100
          SMOKESHOW_GITHUB_CONTEXT: coverage