https://github.com/python/cpython/commit/a2f00d401af98063ea80dbf40f43a3160e242bd9 commit: a2f00d401af98063ea80dbf40f43a3160e242bd9 branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: vstinner <[email protected]> date: 2026-06-01T13:26:30Z summary:
[3.14] gh-149046: fix: correctly handle `str` subclasses in `io.StringIO` (GH-149047) (#150707) gh-149046: fix: correctly handle `str` subclasses in `io.StringIO` (GH-149047) (cherry picked from commit c98773633c97463e35eb51fac81d1095e8061fe0) Co-authored-by: Thomas Kowalski <[email protected]> files: A Misc/NEWS.d/next/Library/2026-04-27-11-12-00.gh-issue-149046.74shDd.rst M Lib/test/test_memoryio.py M Modules/_io/stringio.c diff --git a/Lib/test/test_memoryio.py b/Lib/test/test_memoryio.py index 482b183da23ffa2..3669ac0b038b71b 100644 --- a/Lib/test/test_memoryio.py +++ b/Lib/test/test_memoryio.py @@ -967,6 +967,25 @@ def test_setstate(self): memio.close() self.assertRaises(ValueError, memio.__setstate__, ("closed", "", 0, None)) + def test_write_str_subclass(self): + # Writing a str subclass should use the subclass's unicode data + # directly, not call __str__ on it (which may return a different + # value). gh-149047 + class MyStr(str): + def __str__(self): + return "WRONG" + + s = MyStr("correct") + memio = self.ioclass() + memio.write(s) + self.assertEqual(memio.getvalue(), "correct") + + # Also test the fast path where pos == string_size (STATE_ACCUMULATING) + memio2 = self.ioclass() + memio2.write(MyStr("hello ")) + memio2.write(MyStr("world")) + self.assertEqual(memio2.getvalue(), "hello world") + class CStringIOPickleTest(PyStringIOPickleTest): UnsupportedOperation = io.UnsupportedOperation diff --git a/Misc/NEWS.d/next/Library/2026-04-27-11-12-00.gh-issue-149046.74shDd.rst b/Misc/NEWS.d/next/Library/2026-04-27-11-12-00.gh-issue-149046.74shDd.rst new file mode 100644 index 000000000000000..b05c4222e30fcd2 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-04-27-11-12-00.gh-issue-149046.74shDd.rst @@ -0,0 +1,2 @@ +:mod:`io`: Fix :class:`io.StringIO` serialization: no longer call ``str(obj)`` on :class:`str` +subclasses. Patch by Thomas Kowalski. diff --git a/Modules/_io/stringio.c b/Modules/_io/stringio.c index 0070b7c52d94ac8..8f7801dab96dd1d 100644 --- a/Modules/_io/stringio.c +++ b/Modules/_io/stringio.c @@ -225,7 +225,9 @@ write_str(stringio *self, PyObject *obj) if (self->state == STATE_ACCUMULATING) { if (self->string_size == self->pos) { - if (PyUnicodeWriter_WriteStr(self->writer, decoded)) + // gh-149046: Avoid PyUnicodeWriter_WriteStr() which calls str(obj) + // on str subclasses + if (_PyUnicodeWriter_WriteStr((_PyUnicodeWriter*)self->writer, decoded)) goto fail; goto success; } _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
