Summary

The docstring for fastapi.sse.format_sse_event describes the SSE event terminator as \n\n inside backticks. Because the docstring is a regular Python string (not raw), \n is interpreted as a newline at parse time, so the rendered docstring — e.g. via help(format_sse_event) or any generated reference docs — shows two blank lines between empty backticks instead of the intended \n\n escape sequence.

Escaping the backslashes (\\n\\n in source) makes the rendered text match what was intended.

Before

The result always ends with (the event terminator).

After

The result always ends with \n\n (the event terminator).

Test plan

• python -c "from fastapi.sse import format_sse_event; print(format_sse_event.__doc__)" shows the corrected rendering.
• ruff check fastapi/sse.py passes.
• ruff format fastapi/sse.py --check passes.
• No code-path change — only the __doc__ string content changes; runtime behavior of format_sse_event is identical.