GeezerVison is showing github.com — [3.14] gh-159739: Validate newline replacement in TextIOWrapper.write (GH-160191) by jelle-openai · Pull Request #160487 · python/cpython
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jelle-openai
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Oct 23, 2026
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edited by bedevere-app
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A str subclass can override replace() and return a non-string while TextIOWrapper.write() translates newlines. The C implementation then treats the result as Unicode and can crash. Reject an invalid replacement with TypeError. Backport to 3.15 and 3.14; on 3.14, put the regression test in Lib/test/test_io.py.
(cherry picked from commit c6796a1)
Co-authored-by: Jelle Zijlstra [email protected]
Backport of #160191 to 3.14.
Move the two regression tests into 3.14's Lib/test/test_io.py.
Ran test_io on a free-threaded 3.14 build, including invalid replacement results and callbacks that change the stream state.
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….write (pythonGH-160191)
A str subclass can override replace() and return a non-string while TextIOWrapper.write() translates newlines. The C implementation then treats the result as Unicode and can crash. Reject an invalid replacement with TypeError. Backport to 3.15 and 3.14; on 3.14, put the regression test in Lib/test/test_io.py.
(cherry picked from commit c6796a1)
Co-authored-by: Jelle Zijlstra <[email protected]>
This was referenced Oct 23, 2026
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if (self->encoder == NULL) {
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return _unsupported(self->state, "not writable");
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if (textiowrapper_check_write(self) == NULL) {
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