ENH: Preserve attrs in to_dataframe()

[snowman2]

• [x] Closes #5327
• [x] Tests added
• [x] Passes pre-commit run --all-files
• [x] User visible changes (including notable bug fixes) are documented in whats-new.rst

[dcherian]

Thanks @snowman2

If you're interested, see #3497 for the inverse problem of using pandas attrs when constructing Xarray objects (in a future PR) :)

[max-sixty]

Was there any reason this stalled? It looked like a good start!

[keewis]

I believe the issue is that pandas.DataFrame does not support column attrs (or did not? I didn't check whether that changed since then). DataFrame-level attrs should work, though.

[dcherian]

They were thinking of removing it at one point: https://github.com/pandas-dev/pandas/issues/52166, also https://github.com/dask/dask/issues/11146

perhaps we should punt until someone really really wants it?

[max-sixty]

Yes, looks like the conclusion from the pandas issue is they want to keep it but the support is spotty.

Probably we close this unless someone comes to save it, but I would vote to merge a PR that did this — I can't see a downside...

[giovp]

hi, I just saw that this discussion has been picking up. I work on the framework mentioned in this comment https://github.com/pandas-dev/pandas/issues/52166#issuecomment-2178473375 and we would be very happy if the dataframe-level attrs would be added back to dask-dataframes. We don't use the column-level attrs but do use the df-level attrs. Currently, the solution we implement to use the latest dask is that we ask users to change the configs like so

dask.config.set({'dataframe.query-planning': False})

Would this PR preserve the attrs also in the dask-expr backend?