calling `logging.basicConfig` before `pytest.main()` causes `OSError: [WinError 6] The handle is invalid`

[adabru]

Related: #12876 #5743 #5502 #5282 and probably a lot more

OS: Windows
Python: 3.13.7
pytest: 9.0.2

Calling logging.basicConfig() before pytest.main() and then using logging.info/warn/... inside a test will add lengthy, noisy error logs to the test's stderr capture. This noise is an obstacle in test debugging.

Minimal working example

Run the following in PowerShell:

python --version
# Python 3.13.7
python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install pytest
pip show pytest
# Version: 9.0.2

@"
import logging, pytest

def test_pass():
    logging.warning('warn')

if __name__ == '__main__':
    logging.basicConfig()
    pytest.main()
"@ | Out-File -FilePath "test_main.py" -Encoding utf8
@"
import logging, pytest

@pytest.hookimpl(trylast=True)
def pytest_runtest_logreport(report):
    logging.warning(report.capstderr)
"@ | Out-File -FilePath "conftest.py" -Encoding utf8
python test_main.py
# --- Logging error ---
# Traceback (most recent call last):
#   File "C:\Users\ABrun\.pyenv\pyenv-win\versions\3.13.7\Lib\logging\__init__.py", line 1154, in emit
#     stream.write(msg + self.terminator)
#     ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
# OSError: [WinError 6] The handle is invalid

The package python-html is using the pytest_runtest_logreport hook to generate the html output:

# https://github.com/pytest-dev/pytest-html/blob/e73b6befd69f1852ec1369ef6faab5b1f0286c8e/src/pytest_html/basereport.py#L210-L212
@pytest.hookimpl(trylast=True)
def pytest_runtest_logreport(self, report):

MWE with pytest-html:

python --version
# Python 3.13.7
python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install pytest pytest-html
pip show pytest
# Version: 9.0.2
pip show pytest-html
# Version: 4.2.0

@"
import logging, pytest

def test_pass():
    logging.warning('warn')

if __name__ == '__main__':
    logging.basicConfig()
    pytest.main(['--html=out.html'])
"@ | Out-File -FilePath "test_main.py" -Encoding utf8
python test_main.py
python -c "import re; print(re.search(r';log(.*?-.*?)#34', open('out.html').read()).group(1).replace('\\n', '\n'))"
# --- Logging error ---
# Traceback (most recent call last):
#   File "C:\Users\ABrun\.pyenv\pyenv-win\versions\3.13.7\Lib\logging\__init__.py", line 1154, in emit
#     stream.write(msg + self.terminator)
#     ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
# OSError: [WinError 6] The handle is invalid

A workaround would be appreciated. I have tried the ones from the other issues but they did not prevent that error message. The comment #13720 (comment) mentions caplog. Is there a way to use caplog to avoid that error message?

[RonnyPfannschmidt]

Fd capture needs to be disabled when doin ill advised changes to. The logging config before pytest is in charge

As far as pytest is concerned itbisbin charge of the testing logging setup

We might needs to start warning or triggering errors

[adabru]

Replacing

    pytest.main()

with

    pytest.main(["--capture=sys"])

does prevent that error, thank you! It also works with pytest-html. The default for --capture is fd.

I have to sacrifice the logs from subprocesses, though. They are not captured anymore.

Running pytest is only part of my python program. How can I make sure that the logging in the rest of my program doesn't interfere with pytest? Can I configure a compatible logger with logging.getLogger for that? Can I use another, compatible logging library? Does pytest provide its own logger object?