采用异步生成器或普通生成器/迭代器（带有 `yield` 的函数），然后流式传输响应主体。

{* ../../docs_src/custom_response/tutorial007_py310.py hl[3,16] *}

/// note | 技术细节

一个 `async` 任务只有在到达 `await` 时才能被取消。如果没有 `await`，生成器（带有 `yield` 的函数）无法被正确取消，即使已请求取消也可能继续运行。

由于这个小示例不需要任何 `await` 语句，我们添加 `await anyio.sleep(0)`，给事件循环一个处理取消的机会。

对于大型或无限流，这一点更为重要。

///

/// tip | 提示

与其直接返回 `StreamingResponse`，更推荐遵循 [流式数据](./stream-data.md) 的写法，它更方便并在幕后为你处理取消。

### Files and Async { #files-and-async }

In most cases, file-like objects are not compatible with async and await by default.

For example, they don't have an `await file.read()`, or `async for chunk in file`.

And in many cases, reading them would be a blocking operation (that could block the event loop), because they are read from disk or from the network.

app = FastAPI()


def do_blocking_work(name: str) -> str:
    # Some blocking I/O operation
    return f"Hello {name}"


@app.get("/items/")
async def read_items():
    result = await asyncify(do_blocking_work)(name="World")
    return {"message": result}
```

And run async code inside of blocking sync code with `syncify()`:

```python
from asyncer import syncify
from fastapi import FastAPI

	dynamicTimeoutLogSize              = 16
	maxDuration                        = math.MaxInt64
	maxDynamicTimeout                  = 24 * time.Hour // Never set timeout bigger than this.
)

// timeouts that are dynamically adapted based on actual usage results
type dynamicTimeout struct {
	timeout       int64
	minimum       int64
	entries       int64
	log           [dynamicTimeoutLogSize]time.Duration
	mutex         sync.Mutex

        // When - Multiple threads get and release buffers
        for (int t = 0; t < threadCount; t++) {
            executor.submit(() -> {
                try {
                    startLatch.await();

                    for (int i = 0; i < opsPerThread; i++) {
                        // Get buffer
                        byte[] buffer = BufferCache.getBuffer();

### Archivos y async { #files-and-async }

En la mayoría de los casos, los objetos tipo archivo no son compatibles con `async` y `await` por defecto.

Por ejemplo, no tienen un `await file.read()`, ni un `async for chunk in file`.

Y en muchos casos leerlos sería una operación bloqueante (que podría bloquear el event loop), porque se leen desde disco o desde la red.

---

"_Honestly, what you've built looks super solid and polished. In many ways, it's what I wanted **Hug** to be - it's really inspiring to see someone build that._"

* `seek(offset)`: 파일 내 `offset`(`int`) 위치의 바이트로 이동합니다.
    * 예) `await myfile.seek(0)` 를 사용하면 파일의 시작부분으로 이동합니다.
    * `await myfile.read()` 를 사용한 후 내용을 다시 읽을 때 유용합니다.
* `close()`: 파일을 닫습니다.

상기 모든 메소드들이 `async` 메소드이기 때문에 “await”을 사용하여야 합니다.

예를들어, `async` *경로 처리 함수*의 내부에서 다음과 같은 방식으로 내용을 가져올 수 있습니다:

```Python
contents = await myfile.read()
```

Use `async` *path operations* only when fully certain that the logic called inside is compatible with async and await (it's called with `await`) or that doesn't block.

```python
from fastapi import FastAPI

app = FastAPI()


# Use async def when calling async code
@app.get("/async-items/")
async def read_async_items():
    data = await some_async_library.fetch_items()
    return data

    callback.await(server.url("/a")).assertBody("abc")
    client.newCall(Request.Builder().url(server.url("/b")).build()).enqueue(callback)
    callback.await(server.url("/b")).assertBody("def")
    client.newCall(Request.Builder().url(server.url("/c")).build()).enqueue(callback)
    callback.await(server.url("/c")).assertBody("ghi")