attrs persistance for Pandas

[davetapley]

Pandas 2.10 has ⬇️, but it only works with pyarrow.
If pyarrow isn't installed then if falls back to fastparquet (per docs), and attrs is always loaded as {}.

• Parquet metadata persistence of DataFrame.attrs pandas-dev/pandas#54346

I assume this need a fix here?

[martindurant]

Yes, this can be fixed here. fastparquet does support storing metadata using write(fn, df, ..., custom_metadata=), so if df has there attrs, we can extract them. The whole of this metadata appears in .key_value_metadata when opening the file, so we can restore them.

I am disappointed in pandas that they have once again ignored fastparquet.

Would you like to implement the functionality, @davetapley ?