[SemTiOne]

Captured sys.stdout and sys.stderr now use the encoding and error handler of the streams they replace. When either setting is missing or is not a string, capture falls back to UTF-8 and strict.

Text writes use those settings. Bytes written directly through .buffer are decoded using the selected encoding when captured output is read back, with undecodable bytes replaced.

stdin capture is unchanged. Binary fixtures still return bytes; text written through them is encoded with the replaced streams' encoding and error handler.

Closes #4389.

• Allow maintainers to push and squash when merging my commits. Please uncheck this if you prefer to squash the commits yourself.

[RonnyPfannschmidt]

🤖 Written by Claude Opus 5.5 via Claude Code for the pytest maintainers; I prompted it, it did the work, I read it.

This makes .encoding report the original stream's codec while the buffer still encodes and decodes UTF-8. The attribute then describes a codec the stream does not use. The tests only print() text, which never reads the attribute. One prints 日本語 under PYTHONIOENCODING=latin-1 and expects it to pass, which the real stream would refuse.

#4389 is about code that acts on the attribute. With PYTHONIOENCODING=latin-1:

import sys

def test_it(capsys):
    sys.stdout.buffer.write("café\n".encode(sys.stdout.encoding))
    sys.stdout.flush()
    assert capsys.readouterr().out == "café\n"

• main: passes (the attribute says UTF-8 and the buffer is UTF-8).
• this PR, --capture=sys/tee-sys or capsys: UnicodeDecodeError in CaptureIO.getvalue at teardown, and every following test in the session errors.
• this PR, --capture=fd without capsys: the output silently becomes caf�.

The attribute and the codec have to agree. That means building the capture stream with the replaced stream's encoding/errors and decoding readback with the same codec. This is how cot.capture does it (design note, fd-level install). It is also the direction of #4398.

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Generated by Claude Code

[SemTiOne]

Thanks, I think this addresses your concern. Could you also rerun the ubuntu-pypy3-xdist and ubuntu-py315 jobs? The PyPy job failed in testing/python/raises.py::TestRaises::test_raises_cyclic_reference[with_group], while the Py315 job timed out in testing/test_debugging.py::TestPDB::test_pdb_unittest_postmortem. Both tests are in unchanged files.