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

[Fabrice Meyer]

I just miss type, I wanted to say cfgrib instead of cfdisk. The goal
here was to try makes _get_default_engine_grib returning cfgrib to see
what happen but it ended with a key error as cfgrib isn't in the
writeable_store.

Best regards,

Fabrice

On Fri, 27 Mar 2020 13:13:32 +0000 Alastair McKinstry
<alastair.mckinstry at sceal.ie> wrote:

> Hi,
>
> I shall forward to upstream. It does appear that setting engine=cfgrib
> should not be necessary if the file is a grib file (by extension) and
> cfgrib is present.
>
> I Agree with your point on writable_stores / cfdisk.
>
> Best regards
>
> Alastair
>
>
> On 27/03/2020 12:44, Fabrice Meyer wrote:
> > 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)