BrokenSessionDep = Annotated[Session, Depends(broken_dep_session)]

app = FastAPI()


@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()

    async def app(scope: Scope, receive: Receive, send: Send) -> None:
        session = WebSocket(scope, receive=receive, send=send)

        async def app(scope: Scope, receive: Receive, send: Send) -> None:
            async with AsyncExitStack() as request_stack:
                scope["fastapi_inner_astack"] = request_stack
                async with AsyncExitStack() as function_stack:

送り返す各 JSON アイテムが `Item`（Pydantic モデル）型で、関数が async の場合、戻り値の型を `AsyncIterable[Item]` と宣言できます:

{* ../../docs_src/stream_json_lines/tutorial001_py310.py ln[1:24] hl[9:11,22] *}

戻り値の型を宣言すると、FastAPI はそれを使ってデータを**検証**し、OpenAPI に**ドキュメント化**し、**フィルター**し、Pydantic で**シリアライズ**します。

/// tip | 豆知識

Pydantic は **Rust** 側でシリアライズを行うため、戻り値の型を宣言しない場合に比べて大幅に高い**パフォーマンス**が得られます。

///

        return HTTPException(
            status_code=HTTP_401_UNAUTHORIZED,
            detail="Not authenticated",
            headers=self.make_authenticate_headers(),
        )

    async def __call__(self, request: Request) -> HTTPAuthorizationCredentials | None:
        authorization = request.headers.get("Authorization")
        scheme, credentials = get_authorization_scheme_param(authorization)

// TODO(b/154564140): Move this to its own header. This requires splitting
// c_api_experimental.h
struct TFE_ContextOptions {
  TF_SessionOptions session_options;
  // true if async execution is enabled.
  bool async = false;
  TFE_ContextDevicePlacementPolicy device_placement_policy{
      TFE_DEVICE_PLACEMENT_SILENT};
  // If true, use TFRT backend
  bool use_tfrt = false;

                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()

@app.get("/items/{item_id}", response_model=Item)
async def read_main(item_id: str, x_token: str = Header()):
    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item_id not in fake_db:
        raise HTTPException(status_code=404, detail="Item not found")
    return fake_db[item_id]


@app.post("/items/")
async def create_item(item: Item, x_token: str = Header()) -> Item:

/// tip | 提示

由于 Pydantic 会在**Rust** 端序列化它，相比未声明返回类型，你将获得更高的**性能**。

///

### 非 async 的*路径操作函数* { #non-async-path-operation-functions }

你也可以使用常规的 `def` 函数（没有 `async`），并以同样的方式使用 `yield`。

FastAPI 会确保其正确运行，从而不阻塞事件循环。

由于此时函数不是 async，正确的返回类型应为 `Iterable[Item]`：

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[28:31] hl[29] *}

### 无返回类型 { #no-return-type }

package bandwidth

import (
	"sync"
	"sync/atomic"
	"time"
)

const (
	// betaBucket is the weight used to calculate exponential moving average
	betaBucket = 0.1 // Number of averages considered = 1/(1-betaObject)
)

// bucketMeasurement captures the bandwidth details for one bucket
type bucketMeasurement struct {
	lock                 sync.Mutex

app = FastAPI()


def get_db():
    db = DBSession()
    try:
        yield db
    finally:
        db.close()


DBDep = Annotated[DBSession, Depends(get_db)]


@app.get("/items/")
async def read_items(db: DBDep):
    return db.query(Item).all()
```

Use the scope `"function"` when they should run the exit code after the response data is generated but before the response is sent back to the client.