adding key to df.to_hdf calls to avoid warning

[abostroem]

Closes issue #236
When df.to_hdf is called without specifying that the key is the key, a FutureWarning is issued by Pandas. This fixes both the warning and updates us for future versions of Pandas.

[github-actions]

Thank you!

Thank you for your pull request 😃

🤖 This automated message can help you check the rendered files in your submission for clarity. If you have any questions, please feel free to open an issue in {sandpaper}.

If you have files that automatically render output (e.g. R Markdown), then you should check for the following:

• 🎯 correct output
• 🖼️ correct figures
• ❓ new warnings
• ‼️ new errors

Rendered Changes

🔍 Inspect the changes: https://github.com/datacarpentry/astronomy-python/compare/md-outputs..md-outputs-PR-254

The following changes were observed in the rendered markdown documents:

 03-transform.md | 2 +-
 04-motion.md    | 4 ++--
 md5sum.txt      | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)

What does this mean?

If you have source files that require output and figures to be generated (e.g. R Markdown), then it is important to make sure the generated figures and output are reproducible.

This output provides a way for you to inspect the output in a diff-friendly manner so that it's easy to see the changes that occur due to new software versions or randomisation.

⏱️ Updated at 2025-12-08 23:26:24 +0000