warn at import time if xr.core.options.OPTIONS["keep_attrs"] is False

[dcherian]

Maybe say something like

"cf_xarray works best when xarray keeps attributes by default. Please run xr.set_options(keep_attrs=True)"

This may be annoying though. We should definitely mention this in the docs (#73)

[jthielen]

I think it would be good to include the warning, but perhaps give the option to disable it with a cf-xarray option or environment variable if the user wants keep_attrs to be False.

[dcherian]

but you can't set a cf_xarray option without importing it first which would show a warning ;)

to be clear, this warning will only be shown once at import time not on every operation.

[jthielen]

but you can't set a cf_xarray option without importing it first which would show a warning ;)

to be clear, this warning will only be shown once at import time not on every operation.

Ah, so an environment variable it would have to be!

[dcherian]

turns out the default is "default" so we could also only raise the warning is OPTIONS["keep_attrs"] == "default". So we wouldn't bug anyone who has explicitly opted out of keep_attrs

[jthielen]

turns out the default is "default" so we could also only raise the warning is OPTIONS["keep_attrs"] == "default". So we wouldn't bug anyone who has explicitly opted out of keep_attrs

Even better!

[dcherian]

One (minor) issue with implementing this is that linters will format code to something like

import cf_xarray  # will raise warning here.
import xarray

xr.set_options(keep_attrs=True)

making the warning useless.