```

**Important**: Return types or response models are what filter data ensuring no sensitive information is exposed. And they are used to serialize data with Pydantic (in Rust), this is the main idea that can increase response performance.

The return type doesn't have to be a Pydantic model, it could be a different type, like a list of integers, or a dict, etc.

  - type: input
    id: author-other-languages-experience
    attributes:
      label: "Other Languages Experience"
      description: "What other languages do you have experience with?"
      placeholder: "Go, Python, JS, Rust"
    validations:
      required: false

  - type: checkboxes
    id: related-idea
    attributes:
      label: "Related Idea"
      options:

* **Concis** : diminue la duplication de code. Plusieurs fonctionnalités à partir de chaque déclaration de paramètre. Moins de bugs.
* **Robuste** : obtenez un code prêt pour la production. Avec une documentation interactive automatique.

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip | Порада

Оскільки Pydantic серіалізує це на боці **Rust**, ви отримаєте значно вищу **продуктивність**, ніж якби не оголошували тип повернення.

///

### Не-async *функції операцій шляху* { #non-async-path-operation-functions }

/// tip | Tipp

Da Pydantic es auf der **Rust**-Seite serialisiert, erhalten Sie eine deutlich höhere **Leistung** als wenn Sie keinen Rückgabetyp deklarieren.

///

### Nicht-async *Pfadoperation-Funktionen* { #non-async-path-operation-functions }

import org.jspecify.annotations.Nullable;

/**
 * A series of tests that support asserting that collections cannot be modified, either through
 * direct or indirect means.
 *
 * @author Robert Konigsberg
 */
@GwtCompatible
@NullMarked
public class UnmodifiableCollectionTests {

  public static void assertMapEntryIsUnmodifiable(Entry<?, ?> entry) {
    try {

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip | Consejo

Como Pydantic lo serializará en el lado de **Rust**, obtendrás un **rendimiento** mucho mayor que si no declaras un tipo de retorno.

///

### No async *path operation functions* { #non-async-path-operation-functions }

Si declaras el tipo de retorno, FastAPI lo usará para **validar** los datos, **documentarlos** en OpenAPI, **filtrarlos** y **serializarlos** usando Pydantic.

/// tip | Consejo

Como Pydantic lo serializará en el lado de **Rust**, obtendrás un **rendimiento** mucho mayor que si no declaras un tipo de retorno.

///

### *path operation functions* no-async { #non-async-path-operation-functions }

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip

As Pydantic will serialize it in the **Rust** side, you will get much higher **performance** than if you don't declare a return type.

///

### Non-async *path operation functions* { #non-async-path-operation-functions }

If you declare the return type, FastAPI will use it to **validate** the data, **document** it in OpenAPI, **filter** it, and **serialize** it using Pydantic.

/// tip

As Pydantic will serialize it in the **Rust** side, you will get much higher **performance** than if you don't declare a return type.

///

### Non-async *path operation functions* { #non-async-path-operation-functions }