For example you could have a file `main.py` with:

```Python hl_lines="3"
import os

name = os.getenv("MY_NAME", "World")
print(f"Hello {name} from Python")
```

/// tip

The second argument to <a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> is the default value to return.

                        + "' has been set using a JVM system property which is deprecated. "
                        + "The property can be passed as a Maven argument or in the Maven project configuration file,"
                        + "usually located at ${session.rootDirectory}/.mvn/maven.properties.");
            }
        }
        ArrayList<Path> jars = new ArrayList<>();

///

Das einzig Neue ist `callbacks=invoices_callback_router.routes` als Argument für den *Pfadoperation-Dekorator*. Wir werden als Nächstes sehen, was das ist.

## Dokumentation des Callbacks

Der tatsächliche Callback-Code hängt stark von Ihrer eigenen API-Anwendung ab.

    return (graph instanceof ImmutableValueGraph)
        ? (ImmutableValueGraph<N, V>) graph
        : new ImmutableValueGraph<N, V>(graph);
  }

  /**
   * Simply returns its argument.
   *
   * @deprecated no need to use this
   */
  @Deprecated
  public static <N, V> ImmutableValueGraph<N, V> copyOf(ImmutableValueGraph<N, V> graph) {
    return checkNotNull(graph);
  }

  @Override

	for _, collectorPath := range h.metricsData.collectorPaths {
		if collectorPath.isDescendantOf(path) {
			gatherer := h.metricsData.mgGatherers[collectorPath]

			// For Bucket metrics we need to set the buckets argument inside the
			// metric group, so that it will affect collection. If no buckets
			// are provided, we will not return bucket metrics.
			if bmg, ok := h.metricsData.bucketMGMap[collectorPath]; ok {

	args := &CoreDNS{
		etcdClient: etcdClient,
	}

	for _, setter := range setters {
		setter(args)
	}

	if len(args.domainNames) == 0 || args.domainIPs.IsEmpty() {
		return nil, errors.New("invalid argument")
	}

	// strip ports off of domainIPs
	domainIPsWithoutPorts := args.domainIPs.ApplyFunc(func(ip string) string {
		host, _, err := net.SplitHostPort(ip)
		if err != nil {

  quay.io/minio/minio server /data --console-address ":9001"
```

The command creates a new local directory `~/minio/data` in your user home directory. It then starts the MinIO container with the `-v` argument to map the local path (`~/minio/data`) to the specified virtual container directory (`/data`). When MinIO writes data to `/data`, that data is actually written to the local path `~/minio/data` where it can persist between container restarts.

    return (graph instanceof ImmutableValueGraph)
        ? (ImmutableValueGraph<N, V>) graph
        : new ImmutableValueGraph<N, V>(graph);
  }

  /**
   * Simply returns its argument.
   *
   * @deprecated no need to use this
   */
  @Deprecated
  public static <N, V> ImmutableValueGraph<N, V> copyOf(ImmutableValueGraph<N, V> graph) {
    return checkNotNull(graph);
  }

  @Override

```Python hl_lines="6-7"
{!../../docs_src/path_params/tutorial001.py!}
```

Der Wert des Pfad-Parameters `item_id` wird Ihrer Funktion als das Argument `item_id` übergeben.

Wenn Sie dieses Beispiel ausführen und auf <a href="http://127.0.0.1:8000/items/foo" class="external-link" target="_blank">http://127.0.0.1:8000/items/foo</a> gehen, sehen Sie als Response:

```JSON

```

/// tip | Dica

O parâmetro de consulta `callback_url` usa um tipo Pydantic <a href="https://docs.pydantic.dev/latest/api/networks/" class="external-link" target="_blank">Url</a>.

///

A única coisa nova é o argumento `callbacks=invoices_callback_router.routes` no decorador da *operação de rota*. Veremos o que é isso a seguir.

## Documentando o callback

O código real do callback dependerá muito do seu próprio aplicativo de API.