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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"csv.writer: multi-character lineterminator is truncated to a single byte","articleBody":"## Feature\n\n\u003c!-- What Python feature is missing from RustPython? Give a short description of the feature and how you ran into its absence. --\u003e\n\nFollow-up from #8302 / #8315.\n\n`csv.writer` should accept an arbitrary string as `lineterminator`. RustPython stores it as a single byte, so a multi-character terminator is truncated instead of being emitted in full.\n\n```python\nimport csv, io\nsio = io.StringIO()\ncsv.writer(sio, lineterminator=\"!@#\").writerow([\"a\", \"b\"])\nprint(repr(sio.getvalue()))\n# CPython:    'a,b!@#'\n# RustPython: 'a,b!'\n```\n\nBecause of this, `test_write_lineterminator` (Lib/test/test_csv.py) is marked `@unittest.expectedFailure` — it fails only on the `'!@#'` subcase.\n\nScope is limited to the multi-character `lineterminator`. Left as separate follow-ups: lineterminator validation parity, non-ASCII `delimiter`/`quotechar`/`escapechar` (see #8310), and reader semantics (CPython's reader ignores `lineterminator` and only recognizes CR/LF).\n\n## Python Documentation or reference to CPython source code\n\n\u003c!-- Give a link to the feature in the CPython documentation (https://docs.python.org/3/) in order to assist in its implementation. --\u003e\n\nhttps://docs.python.org/3/library/csv.html#csv.Dialect.lineterminator\n\n\u003csub\u003eDrafted with AI assistance (Claude Code), reviewed by me.\u003c/sub\u003e","author":{"url":"https://github.com/jinmay","@type":"Person","name":"jinmay"},"datePublished":"2026-07-19T12:10:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/8322/RustPython/issues/8322"}