def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>或者使用 <code>async def</code>...</summary>

如果你的代码里会出现 `async` / `await`，请使用 `async def`：

```Python hl_lines="9  14"
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def read_root():
    return {"Hello": "World"}

  c. The disclaimer of warranties and limitation of liability provided
     above shall be interpreted in a manner that, to the extent
     possible, most closely approximates an absolute disclaimer and
     waiver of all liability.


Section 6 -- Term and Termination.

  a. This Public License applies for the term of the Copyright and
     Similar Rights licensed here. However, if You fail to comply with

Nesse caso, a função de tarefa gravará em um arquivo (simulando o envio de um e-mail).

E como a operação de gravação não usa `async` e `await`, definimos a função com `def` normal:

```Python hl_lines="6-9"
{!../../docs_src/background_tasks/tutorial001.py!}
```

## Adicionar a tarefa em segundo plano

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

## Add the background task

        transformer.setOutputProperty(OutputKeys.METHOD, "xml");

        final StringWriter writer = new StringWriter();
        final StreamResult result = new StreamResult(writer);

        final DOMSource source = new DOMSource(node);
        transformer.transform(source, result);

        return writer.toString();
    }

    public void test_getChildUrlRules() {

                logger.error("Failed to update suggest index.", t);
                exitCode.set(1);
                latch.countDown();
            });

            try {
                latch.await();
            } catch (final InterruptedException ignore) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Interrupted.", ignore);
                }
                exitCode.set(1);

pkg bufio, method (*Writer) AvailableBuffer() []uint8
pkg bufio, method (ReadWriter) AvailableBuffer() []uint8
pkg bytes, func Cut([]uint8, []uint8) ([]uint8, []uint8, bool)
pkg bytes, func Title //deprecated
pkg crypto/tls, method (*Conn) NetConn() net.Conn
pkg crypto/tls, type Config struct, PreferServerCipherSuites //deprecated
pkg crypto/x509, method (*CertPool) Subjects //deprecated
pkg debug/buildinfo, func Read(io.ReaderAt) (*debug.BuildInfo, error)

      assertEquals(cancelMode == INTERRUPT, Thread.interrupted())
    }
    responseBody.close()
    assertEquals(if (connectionType == H2) 1 else 0, client.connectionPool.connectionCount())

    cancelLatch.await()

    val events = listener.eventSequence.filter { isConnectionEvent(it) }.map { it.name }
    listener.clearAllEvents()

    assertThat(events).startsWith("CallStart", "ConnectStart", "ConnectEnd", "ConnectionAcquired")

{!../../docs_src/app_testing/tutorial001.py!}
```

/// tip | "Dica"

Observe que as funções de teste são `def` normais, não `async def`.

E as chamadas para o cliente também são chamadas normais, não usando `await`.

Isso permite que você use `pytest` diretamente sem complicações.

///

/// note | "Detalhes técnicos"

Você também pode usar `from starlette.testclient import TestClient`.

/**
 * An {@link InputStream} that converts characters from a {@link Reader} into bytes using an
 * arbitrary Charset.
 *
 * <p>This is an alternative to copying the data to an {@code OutputStream} via a {@code Writer},
 * which is necessarily blocking. By implementing an {@code InputStream} it allows consumers to
 * "pull" as much data as they can handle, which is more convenient when dealing with flow
 * controlled, async APIs.
 *