@app.get("/items/stream-sse-event", response_class=EventSourceResponse)
async def sse_items_event():
    yield ServerSentEvent(data="hello", event="greeting", id="1")
    yield ServerSentEvent(data={"key": "value"}, event="json-data", id="2")
    yield ServerSentEvent(comment="just a comment")
    yield ServerSentEvent(data="retry-test", retry=5000)


@app.get("/items/stream-mixed", response_class=EventSourceResponse)

```python
from collections.abc import AsyncIterable

from fastapi import FastAPI
from fastapi.sse import EventSourceResponse, ServerSentEvent

app = FastAPI()


@app.get("/events", response_class=EventSourceResponse)
async def stream_events() -> AsyncIterable[ServerSentEvent]:
    yield ServerSentEvent(data={"status": "started"}, event="status", id="1")

async def stream_items(
    last_event_id: Annotated[int | None, Header()] = None,
) -> AsyncIterable[ServerSentEvent]:
    start = last_event_id + 1 if last_event_id is not None else 0
    for i, item in enumerate(items):
        if i < start:
            continue

from fastapi.sse import EventSourceResponse, ServerSentEvent
from pydantic import BaseModel

app = FastAPI()


class Prompt(BaseModel):
    text: str


@app.post("/chat/stream", response_class=EventSourceResponse)
async def stream_chat(prompt: Prompt) -> AsyncIterable[ServerSentEvent]:
    words = prompt.text.split()
    for word in words:
        yield ServerSentEvent(data=word, event="token")

from collections.abc import AsyncIterable

from fastapi import FastAPI
from fastapi.sse import EventSourceResponse, ServerSentEvent

app = FastAPI()


@app.get("/logs/stream", response_class=EventSourceResponse)
async def stream_logs() -> AsyncIterable[ServerSentEvent]:
    logs = [
        "2025-01-01 INFO  Application started",
        "2025-01-01 DEBUG Connected to database",
        "2025-01-01 WARN  High memory usage detected",
    ]

你也可以省略返回类型。FastAPI 将使用 [`jsonable_encoder`](./encoder.md) 转换数据并发送。

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[34:37] hl[35] *}

## `ServerSentEvent` { #serversentevent }

如果你需要设置 `event`、`id`、`retry` 或 `comment` 等 SSE 字段，你可以 yield `ServerSentEvent` 对象，而不是直接返回数据。

从 `fastapi.sse` 导入 `ServerSentEvent`：

{* ../../docs_src/server_sent_events/tutorial002_py310.py hl[4,26] *}

`data` 字段始终会被编码为 JSON。你可以传入任何可被序列化为 JSON 的值，包括 Pydantic 模型。

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[34:37] hl[35] *}

## `ServerSentEvent` { #serversentevent }

`event`, `id`, `retry`, `comment` 같은 SSE 필드를 설정해야 한다면, 일반 데이터 대신 `ServerSentEvent` 객체를 `yield`할 수 있습니다.

`ServerSentEvent`는 `fastapi.sse`에서 임포트합니다:

{* ../../docs_src/server_sent_events/tutorial002_py310.py hl[4,26] *}

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[34:37] hl[35] *}

## `ServerSentEvent` { #serversentevent }

`event`、`id`、`retry`、`comment` などの SSE フィールドを設定する必要がある場合は、生データの代わりに `ServerSentEvent` オブジェクトを `yield` できます。

`ServerSentEvent` は `fastapi.sse` からインポートします:

{* ../../docs_src/server_sent_events/tutorial002_py310.py hl[4,26] *}

## 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.

                def _serialize_sse_item(item: Any) -> bytes:
                    if isinstance(item, ServerSentEvent):
                        # User controls the event structure.
                        # Serialize the data payload if present.
                        # For ServerSentEvent items we skip stream_item_field
                        # validation (the user may mix types intentionally).