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📝 Add await in StreamingResponse code example to allow cancellation #14681

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tiangolo merged 3 commits into from
Feb 27, 2026
+13 −1
Merged

📝 Add await in StreamingResponse code example to allow cancellation #14681

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7f49f35
fix StreamingResponse example
casperdcl Jan 10, 2026
1ce08a4
🔁 Merge branch 'master' into pr/casperdcl/14681
tiangolo Feb 27, 2026
163e35c
📝 Tweak the docs text and example
tiangolo Feb 27, 2026
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12 changes: 11 additions & 1 deletion docs/en/docs/advanced/custom-response.md
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Expand Up @@ -167,7 +167,17 @@ You can also use the `status_code` parameter combined with the `response_class`

Takes an async generator or a normal generator/iterator and streams the response body.

{* ../../docs_src/custom_response/tutorial007_py310.py hl[2,14] *}
{* ../../docs_src/custom_response/tutorial007_py310.py hl[3,16] *}

/// note | Technical Details

An `async` task can only be cancelled when it reaches an `await`. If there is no `await`, the generator (function with `yield`) can not be cancelled properly and may keep running even after cancellation is requested.

Since this small example does not need any `await` statements, we add an `await anyio.sleep(0)` to give the event loop a chance to handle cancellation.

This would be even more important with large or infinite streams.

///

#### Using `StreamingResponse` with file-like objects { #using-streamingresponse-with-file-like-objects }

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2 changes: 2 additions & 0 deletions docs_src/custom_response/tutorial007_py310.py
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@@ -1,3 +1,4 @@
import anyio
from fastapi import FastAPI
from fastapi.responses import StreamingResponse

Expand All @@ -7,6 +8,7 @@
async def fake_video_streamer():
for i in range(10):
yield b"some fake video bytes"
await anyio.sleep(0)


@app.get("/")
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