Y tu aplicación de **FastAPI** también podría estar compuesta de varios archivos/módulos, etc.

### Archivo de aplicación **FastAPI**

Digamos que tienes una estructura de archivos como se describe en [Aplicaciones Más Grandes](bigger-applications.md){.internal-link target=_blank}:

```
.
├── app
│   ├── __init__.py
│   └── main.py
```

En el archivo `main.py` tienes tu aplicación de **FastAPI**:

That means that, clients using your API don't have to check if the value exists or not, they can **assume the field will always be there**, but just that in some cases it will have the default value of `None`.

The way to describe this in OpenAPI, is to mark that field as **required**, because it will always be there.

Because of that, the JSON Schema for a model can be different depending on if it's used for **input or output**:

// metrics group.
func (mg *MetricsGroup) IsBucketMetricsGroup() bool {
	return mg.bucketLoader != nil
}

// Describe - implements prometheus.Collector interface.
func (mg *MetricsGroup) Describe(ch chan<- *prometheus.Desc) {
	for _, desc := range mg.Descriptors {
		ch <- desc.toPromDesc(mg.CollectorPath.metricPrefix(), mg.ExtraLabels)
	}
}

    listeners.add(new PerListenerQueue<>(listener, executor));
  }

  /**
   * Enqueues an event to be run on currently known listeners.
   *
   * <p>The {@code toString} method of the Event itself will be used to describe the event in the
   * case of an error.
   *
   * @param event the callback to execute on {@link #dispatch}
   */
  public void enqueue(Event<L> event) {
    enqueueHelper(event, event);
  }

  /**

* `description`: un `str` con una breve descripción de la etiqueta. Puede tener Markdown y se mostrará en la interfaz de documentación.
* `externalDocs`: un `dict` que describe documentación externa con:
    * `description`: un `str` con una breve descripción para la documentación externa.
    * `url` (**requerido**): un `str` con la URL para la documentación externa.

### Crear metadata para etiquetas

	// This function is a reference (re-)implementation of
	// decrypted range computation, written solely for the purpose
	// of the unit tests.
	//
	// `s` gives the decrypted part sizes, and the other
	// parameters describe the desired read segment. When
	// `isFromEnd` is true, `skipLen` argument is ignored.
	decryptedRangeRef := func(s []int64, skipLen, readLen int64, isFromEnd bool) (o, l, skip int64, sn uint32, ps int) {
		oSize := lsum(s)

         * repository's layout to allow pointing at artifacts within the repository. Unfortunately,
         * DefaultRepositoryLayout does not correctly describe the layout of a local repository which unlike a remote
         * repository never uses timestamps in the filename of a snapshot artifact. The discrepancy gets notable when a

* Try to make the title descriptive about what it achieves. If it's a feature, try to describe it, for example `Add support for teleporting` instead of `Create TeleportAdapter class`.
* Do not finish the title with a period (`.`).

{* ../../docs_src/behind_a_proxy/tutorial004.py hl[9] *}

y entonces no lo incluirá en el esquema de OpenAPI.

## Montando una sub-aplicación

Si necesitas montar una sub-aplicación (como se describe en [Aplicaciones secundarias - Monturas](sub-applications.md){.internal-link target=_blank}) mientras usas un proxy con `root_path`, puedes hacerlo normalmente, como esperarías.

    }

    /**
     * Creates a {@link ReentrantLock} with the given fairness policy and rank. The values returned
     * by {@link Enum#getDeclaringClass()} and {@link Enum#name()} are used to describe the lock in
     * warning or exception output.
     *
     * @throws IllegalStateException If the factory has already created a {@code Lock} with the
     *     specified rank.
     */