async def custom_http_exception_handler(request, exc):
    print(f"OMG! An HTTP error!: {repr(exc)}")
    return await http_exception_handler(request, exc)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
    print(f"OMG! The client sent invalid data!: {exc}")
    return await request_validation_exception_handler(request, exc)


@app.get("/items/{item_id}")

    exit_limiter = CapacityLimiter(1)
    try:
        yield await run_in_threadpool(cm.__enter__)
    except Exception as e:
        ok = bool(
            await anyio.to_thread.run_sync(
                cm.__exit__, type(e), e, e.__traceback__, limiter=exit_limiter
            )
        )
        if not ok:
            raise e
    else:
        await anyio.to_thread.run_sync(

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket, session: SessionDep):
    await websocket.accept()
    for item in session:
        await websocket.send_text(f"{item}")


@app.websocket("/ws-broken")
async def websocket_endpoint_broken(websocket: WebSocket, session: BrokenSessionDep):
    await websocket.accept()
    for item in session:
        await websocket.send_text(f"{item}")  # pragma no cover


client = TestClient(app)

    // Now give the get() thread time to finish:
    assertTrue(earlyListener.wasRun.await(1, SECONDS));

    // Now test an additional addListener call, which will be run in-thread:
    RecordingRunnable lateListener = new RecordingRunnable();
    listenable.addListener(lateListener, directExecutor());
    assertTrue(lateListener.wasRun.await(1, SECONDS));
  }

  public void testAdapters_nullChecks() throws Exception {

## `async` 和 `await` { #async-and-await }

現代 Python 版本提供一種非常直觀的方式定義非同步程式碼。這使得它看起來就像正常的「順序」程式碼，並在適當的時機替你「等待」。

當某個操作需要等待才能回傳結果，並且支援這些新的 Python 特性時，你可以像這樣編寫程式碼：

```Python
burgers = await get_burgers(2)
```

這裡的關鍵是 `await`。它告訴 Python 必須等待 ⏸ `get_burgers(2)` 完成它的工作 🕙， 然後將結果儲存在 `burgers` 中。如此，Python 就可以在此期間去處理其他事情 🔀 ⏯ （例如接收另一個請求）。

要讓 `await` 運作，它必須位於支持非同步功能的函式內。為此，只需使用 `async def` 宣告函式：

app = FastAPI()


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


@app.websocket("/ws")
async def websocket(websocket: WebSocket):
    await websocket.accept()
    await websocket.send_json({"msg": "Hello WebSocket"})
    await websocket.close()


def test_read_main():
    client = TestClient(app)
    response = client.get("/")
    assert response.status_code == 200

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

有关路径操作函数的 `async def` 语法以及异步代码、并发和并行的一些背景知识。

## 赶时间吗？ { #in-a-hurry }

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

如果你正在使用第三方库，它们会告诉你使用 `await` 关键字来调用它们，就像这样：

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

然后，通过 `async def` 声明你的 *路径操作函数*：

```Python hl_lines="2"
@app.get('/')
async def read_results():
    results = await some_library()

        original_route_handler = super().get_route_handler()

        async def custom_route_handler(request: Request) -> Response:
            try:
                return await original_route_handler(request)
            except RequestValidationError as exc:
                body = await request.body()
                detail = {"errors": exc.errors(), "body": body.decode()}
                raise HTTPException(status_code=422, detail=detail)

			}
			f.Close()
		}

		bs, err := os.ReadFile(goldenFile)
		if err != nil {
			t.Fatalf("opening golden.txt for package %q: %v", fi.Name(), err)
		}
		wanted := strings.Split(string(bs), "\n")
		slices.Sort(wanted)
		for _, feature := range wanted {
			if feature == "" {
				continue
			}
			_, ok := w.features[feature]
			if !ok {
				t.Errorf("package %s: missing feature %q", fi.Name(), feature)
			}

	var zb0001 uint32
	zb0001, err = dc.ReadArrayHeader()
	if err != nil {
		err = msgp.WrapError(err)
		return
	}
	if zb0001 != uint32(sizeLastElemMarker) {
		err = msgp.ArrayError{Wanted: uint32(sizeLastElemMarker), Got: zb0001}
		return
	}
	for za0001 := range z {
		var field []byte
		_ = field
		var zb0002 uint32
		zb0002, err = dc.ReadMapHeader()
		if err != nil {