# Concurrency and async / await { #concurrency-and-async-await }

Details about the `async def` syntax for *path operation functions* and some background about asynchronous code, concurrency, and parallelism.

## In a hurry? { #in-a-hurry }

<abbr title="too long; didn't read"><strong>TL;DR:</strong></abbr>

If you are using third party libraries that tell you to call them with `await`, like:

```Python
results = await some_library()
```

Pero primero, vamos a revisar algunos pequeños conceptos.

## ¿Con prisa? { #in-a-hurry }

Si no te importan ninguno de estos términos y solo necesitas agregar seguridad con autenticación basada en nombre de usuario y contraseña *ahora mismo*, salta a los siguientes capítulos.

## OAuth2 { #oauth2 }

 * class. Similarly, if you know that a given string represents a domain name, use {@link
 * InternetDomainName} rather than this class.
 *
 * @author Craig Berry
 * @since 5.0
 */
@J2ktIncompatible
@GwtIncompatible
public final class HostSpecifier {

  private final String canonicalForm;

  private HostSpecifier(String canonicalForm) {

You could also define it as a normal function instead of `async def`:

{* ../../docs_src/first_steps/tutorial003_py39.py hl[7] *}

/// note

If you don't know the difference, check the [Async: *"In a hurry?"*](../async.md#in-a-hurry){.internal-link target=_blank}.

///

### Step 5: return the content { #step-5-return-the-content }

{* ../../docs_src/first_steps/tutorial001_py39.py hl[8] *}

    return {"item_id": item_id, "q": q}
```

**Примітка**:

Стикнувшись з проблемами, не зайвим буде ознайомитися з розділом _"In a hurry?"_ про <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank">`async` та `await` у документації</a>.

</details>

### Запустіть

Запустіть server з:

<div class="termy">

```console

Manuilov, gerbauz, Guillaume Klein, Guozhong Zhuang, Harry Slatyer, Harsh188,
henri, Henri Woodcock, Hiran Sarkar, Hollow Man, Håkon Sandsmark, I Wayan
Dharmana, icysapphire, Ikko Ashimine, Jab Hofmeier, Jack Hessel, Jacob Valdez,
Jakub Jatczak, James Bernardi, Jared Smolens, Jason Zaman, jedlimlx, Jenny
Plunkett, Jens Elofsson, Jerry Shih, jgehw, Jia Fu Low, Jim Fisher, jpodivin,

 * them as a {@link String}. Example:
 *
 * {@snippet :
 * Joiner joiner = Joiner.on("; ").skipNulls();
 *  . . .
 * return joiner.join("Harry", null, "Ron", "Hermione");
 * }
 *
 * <p>This returns the string {@code "Harry; Ron; Hermione"}. Note that all input elements are
 * converted to strings using {@link Object#toString()} before being appended.
 *

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

**Note**:

如果你不知道是否会用到，可以查看文档的 _"In a hurry?"_ 章节中 <a href="https://fastapi.tiangolo.com/zh/async/#in-a-hurry" target="_blank">关于 `async` 和 `await` 的部分</a>。

</details>

### 运行

通过以下命令运行服务器：

<div class="termy">

```console
$ uvicorn main:app --reload

{* ../../docs_src/first_steps/tutorial003.py hl[7] *}

/// note | Not

Eğer farkı bilmiyorsanız, [Async: *"Aceleniz mi var?"*](../async.md#in-a-hurry){.internal-link target=_blank} sayfasını kontrol edebilirsiniz.

///

### Adım 5: İçeriği Geri Döndürün

{* ../../docs_src/first_steps/tutorial001.py hl[8] *}

Es spielt keine Rolle. **FastAPI** weiß, was zu tun ist.

/// note | Hinweis

Wenn Ihnen das nichts sagt, lesen Sie den [Async: *„In Eile?“*](../../async.md#in-a-hurry){.internal-link target=_blank}-Abschnitt über `async` und `await` in der Dokumentation.

///

## Integriert in OpenAPI { #integrated-with-openapi }