Bug#955015: python3-xarray: Backend api engine grib broken

[Fabrice Meyer]

Just adding a detail, to avoid messing with xarray code, you just need
to call to_netcdf with an engine define in your parameters. It is just
the default engine selection which appears to be broken on this version
of xarray (and also in stable).

Regards


Le 26/03/2020 à 21:07, Fabrice Meyer a écrit :
> Package: python3-xarray
> Version: 0.15.0-3
> Severity: important
>
> Dear Maintainer,
>
> I was trying to use to_netcdf() located in /usr/lib/python3/dist-packages/xarray/backends/api.py on a grib file without specifying the engine and it appears that the default engine selection end up on grib engine.
>
> So _get_default_engine calls _get_default_engine_grib as we have a grib file but this function always raise a ValueError even if cfgrib import succeed but anyway, there is a real issue with this function as it is returning nothing while _get_default_engine is expecting an engine.
> If we try to, somehow, makes _get_default_engine_grib return cfdisk as engine, it will still fail as cfgrib is absent of the WRITEABLE_STORES bellow but even if it would have been present, cfgrib does not implement a writeable store.
>
> WRITEABLE_STORES: Dict[str, Callable] = {
>     "netcdf4": backends.NetCDF4DataStore.open,
>     "scipy": backends.ScipyDataStore,
>     "h5netcdf": backends.H5NetCDFStore.open,
> }
>
> I'm quite new dealing with xarray but I think grib engine seems to be on work in progress or something and doesn't look ready yet.
>
> In order to get the job done, I tryed to make _get_default_engine_grib returning "netcdf4" based on observation on an older implementation of xarray (0.10.2-1). This "hack" worked but it is really dirty. 
>
> Could you please dig a bit more and fix this issue?
>
> Best regards, and thank you for all job done maintaining theses packages.
>
>
> -- System Information:
> Debian Release: bullseye/sid
>   APT prefers stable-updates
>   APT policy: (500, 'stable-updates'), (500, 'unstable'), (500, 'testing'), (500, 'stable')
> Architecture: amd64 (x86_64)
>
> Kernel: Linux 4.19.0-8-amd64 (SMP w/1 CPU core)
> Kernel taint flags: TAINT_CRAP
> Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE=fr_FR.UTF-8 (charmap=UTF-8)
> Shell: /bin/sh linked to /bin/dash
> Init: systemd (via /run/systemd/system)
> LSM: AppArmor: enabled
>
> Versions of packages python3-xarray depends on:
> ii  python3         3.8.2-2
> ii  python3-numpy   1:1.17.4-5
> ii  python3-pandas  0.25.3+dfsg-7
>
> Versions of packages python3-xarray recommends:
> ii  python3-bottleneck  1.2.1+ds1-2+b1
> ii  python3-dask        2.11.0+dfsg-1
> ii  python3-h5netcdf    0.7.1-1
> ii  python3-netcdf4     1.5.3-1+b2
> ii  python3-zarr        2.4.0+ds-1
>
> Versions of packages python3-xarray suggests:
> pn  python-xarray-doc   <none>
> pn  python3-cartopy     <none>
> ii  python3-matplotlib  3.2.1-1
> pn  python3-pydap       <none>
> pn  python3-rasterio    <none>
> ii  python3-scipy       1.3.3-3
> pn  python3-seaborn     <none>
> ii  python3-toolz       0.9.0-1
>
> -- no debconf information