`setDaemon()` Deprecation warning for `to_image`

[huonw]

If one executes to_image with Python 3.10 or greater, there is deprecation warning about setDaemon:

from plotly.graph_objs import Figure
Figure().to_image()

.../.venv/lib/python3.10/site-packages/kaleido/scopes/base.py:188: DeprecationWarning:

setDaemon() is deprecated, set the daemon attribute instead

This appears when warnings are enabled, such as python -W default ... or running tests under pytest.

All-in-one reproducer:

# do it all in a temporary directory/venv
cd $(mktemp -d)
python3.10 -m venv .venv

# install all dependencies
.venv/bin/python -m pip install kaleido==0.2.1 plotly==5.21.0 tenacity==8.2.3 packaging==24.0

# BUG: run to_image, with warnings enabled:
.venv/bin/python -W default -c 'from plotly.graph_objs import Figure; Figure().to_image()'
# DeprecationWarning: setDaemon() is deprecated, set the daemon attribute instead

Based on https://github.com/plotly/Kaleido/issues/171, this can probably be resolved by doing a new release of Kaleido to PyPI & conda, since https://github.com/plotly/Kaleido/pull/146 appears to fix it in the unreleased code on the master branch.

Alternatively, if Kaleido is unmaintained (and thus may stop working with future Python versions), maybe Plotly.py needs to support another engine?

Thanks for Plotly!