### Dependencies with `yield` and `StreamingResponse`, Technical Details { #dependencies-with-yield-and-streamingresponse-technical-details }

Before FastAPI 0.118.0, if you used a dependency with `yield`, it would run the exit code after the *path operation function* returned but right before sending the response.

import anyio
import pytest
from fastapi import FastAPI
from fastapi.responses import StreamingResponse

pytestmark = [
    pytest.mark.anyio,
    pytest.mark.filterwarnings("ignore::pytest.PytestUnraisableExceptionWarning"),
]


app = FastAPI()


@app.get("/stream-raw", response_class=StreamingResponse)
async def stream_raw() -> AsyncIterable[str]:

### `yield` と `StreamingResponse` を伴う依存関係、技術詳細 { #dependencies-with-yield-and-streamingresponse-technical-details }

FastAPI 0.118.0 より前では、`yield` を使う依存関係を使用すると、*path operation 関数* が戻ってからレスポンス送信直前に終了コードが実行されていました。

これは、レスポンスがネットワーク上を移動するのを待っている間に、不要にリソースを保持しないようにする意図でした。

この変更により、`StreamingResponse` を返す場合、`yield` を持つ依存関係の終了コードはすでに実行されていることになりました。

```python
from fastapi.responses import (
    FileResponse,
    HTMLResponse,
    JSONResponse,
    ORJSONResponse,
    PlainTextResponse,
    RedirectResponse,
    Response,
    StreamingResponse,
    UJSONResponse,
)
```

## FastAPI Responses

There were a couple of custom FastAPI response classes that were intended to optimize JSON performance.

from typing import Annotated, Any

from annotated_doc import Doc
from pydantic import AfterValidator, BaseModel, Field, model_validator
from starlette.responses import StreamingResponse

# Canonical SSE event schema matching the OpenAPI 3.2 spec
# (Section 4.14.4 "Special Considerations for Server-Sent Events")
_SSE_EVENT_SCHEMA: dict[str, Any] = {
    "type": "object",
    "properties": {
        "data": {"type": "string"},

import json

import pytest
from fastapi import BackgroundTasks, Depends, FastAPI
from fastapi.responses import StreamingResponse
from fastapi.testclient import TestClient

app = FastAPI()
state = {
    "/async": "asyncgen not started",
    "/sync": "generator not started",
    "/async_raise": "asyncgen raise not started",
    "/sync_raise": "generator raise not started",
    "context_a": "not started a",
    "context_b": "not started b",

---

You can also use the `status_code` parameter combined with the `response_class` parameter:

{* ../../docs_src/custom_response/tutorial006c_py310.py hl[2,7,9] *}

### `StreamingResponse` { #streamingresponse }

Takes an async generator or a normal generator/iterator (a function with `yield`) and streams the response body.

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

在此情況下，所使用的 `status_code` 會是 `RedirectResponse` 的預設值 `307`。

---

你也可以同時搭配 `status_code` 與 `response_class` 參數：

{* ../../docs_src/custom_response/tutorial006c_py310.py hl[2,7,9] *}

### `StreamingResponse` { #streamingresponse }

接收一個 async 產生器或一般的產生器／疊代器（帶有 `yield` 的函式），並以串流方式傳送回應本文。

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

/// note | 技術細節

## Streaming (JSON Lines, SSE, bytes)

See [the streaming reference](references/streaming.md) for JSON Lines, Server-Sent Events (`EventSourceResponse`, `ServerSentEvent`), and byte streaming (`StreamingResponse`) patterns.

## Tooling

See [the other tools reference](references/other-tools.md) for details on uv, Ruff, ty for package management, linting, type checking, formatting, etc.

## Other Libraries

## «`StreamingResponse` с `yield`» { #a-streamingresponse-with-yield }

Если вы укажете `response_class=StreamingResponse` в своей *функции-обработчике пути*, вы можете использовать `yield`, чтобы по очереди отправлять каждый чанк данных.

{* ../../docs_src/stream_data/tutorial001_py310.py ln[1:23] hl[20,23] *}