#### `Optional`

`Optional` bir değişkenin `str`gibi bir tipi olabileceğini ama isteğe bağlı olarak tipinin `None` olabileceğini belirtir:

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

`str` yerine `Optional[str]` kullanmak editorün bu değerin her zaman `str` tipinde değil bazen `None` tipinde de olabileceğini belirtir ve hataları tespit etmemizde yardımcı olur.

#### Generic tipler

              </models>
              <version>2.0.0</version>
            </configuration>
          </execution>
          <execution>
            <id>modello-site-docs</id>
            <phase>none</phase>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>com.github.siom79.japicmp</groupId>
        <artifactId>japicmp-maven-plugin</artifactId>

				// The queue should always have at least one entry left for this to work.
				outputQueue = outputQueue[:len(outputQueue)+1]
				if t := outputQueue[len(outputQueue)-1]; t != nil {
					// If the output record is already set, we reuse it.
					outputRecord = t
					outputRecord.Reset()
				} else {
					// Create new one
					outputRecord = s3Select.outputRecord()

   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.
   * @throws NullPointerException if any element in the stream is {@code null}.
   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")

								<em class="fa fa-cog"> <span class="sr-only"><la:message
										key="labels.header_form_option_btn" /></span>
							</button>
						</span>
					</div>
				</div>
				<ul class="nav navbar-nav d-none d-md-flex">
					<c:if test="${eoled}">
						<li class="nav-item" data-toggle="tooltip" data-placement="left" title="<la:message key="labels.eol_error" />">

								<em class="fa fa-cog"> <span class="sr-only"><la:message
										key="labels.header_form_option_btn" /></span>
							</button>
						</span>
					</div>
				</div>
				<ul class="nav navbar-nav d-none d-md-flex">
					<c:if test="${eoled}">
						<li class="nav-item" data-toggle="tooltip" data-placement="left" title="<la:message key="labels.eol_error" />">

		if waypointName == "" {
			waypointName = constants.DefaultNamespaceWaypoint
		} else if waypointName == "none" {
			return nil, fmt.Errorf("invalid name provided for waypoint, 'none' is a reserved value")
		}
		gw := gateway.Gateway{
			TypeMeta: metav1.TypeMeta{
				Kind:       gvk.KubernetesGateway_v1.Kind,
				APIVersion: gvk.KubernetesGateway_v1.GroupVersion(),

re(e,t){for(var n,r,i,o,a,s,u,l=[],c=0,f=e.length;c<f;c++)(r=e[c]).style&&(n=r.style.display,t?("none"===n&&(l[c]=_.get(r,"display")||null,l[c]||(r.style.display="")),""===r.style.display&&ee(r)&&(l[c]=(u=a=o=void 0,a=(i=r).ownerDocument,s=i.nodeName,(u=ne[s])||(o=a.body.appendChild(a.createElement(s)),u=ce.css(o,"display"),o.parentNode.removeChild(o),"none"===u&&(u="block"),ne[s]=u)))):"none"!==n&&(l[c]="none",_.set(r,"display",n)));for(c=0;c<f;c++)null!=l[c]&&(e[c].style.display=l[c]);return e}ce.f...

## Retrying Requests

Sometimes connections fail: either a pooled connection was stale and disconnected, or the webserver itself couldn’t be reached. OkHttp will retry the request with a different route if one is available.

def test_get_starlette_item_not_found():
    response = client.get("/starlette-items/bar")
    assert response.status_code == 404, response.text
    assert response.headers.get("x-error") is None
    assert response.json() == {"detail": "Item not found"}


def test_no_body_status_code_exception_handlers():
    response = client.get("/http-no-body-statuscode-exception")
    assert response.status_code == 204