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Cannot open dataset with empty list units
What happened?
I found myself using a netcdf with empty units and by using xarray i was unable to use open_dataset due to the parsing of cf conventions. I reproduce the bug, and it happens in a particular situation when the units is an empty list (See Minimal Complete Verifiable Example)
What did you expect to happen?
To parse the units attribute as an empty string ?
Minimal Complete Verifiable Example
temp = 15 + 8 * np.random.randn(2, 2, 3)
precip = 10 * np.random.rand(2, 2, 3)
lon = [[-99.83, -99.32], [-99.79, -99.23]]
lat = [[42.25, 42.21], [42.63, 42.59]]
# for real use cases, its good practice to supply array attributes such as
# units, but we won't bother here for the sake of brevity
ds = xr.Dataset(
{
"temperature": (["x", "y", "time"], temp),
"precipitation": (["x", "y", "time"], precip),
},
coords={
"lon": (["x", "y"], lon),
"lat": (["x", "y"], lat),
"time": pd.date_range("2014-09-06", periods=3),
"reference_time": pd.Timestamp("2014-09-05"),
},
)
ds.temperature.attrs["units"] = []
ds.to_netcdf("test.nc")
ds = xr.open_dataset("test.nc")
ds.close()
MVCE confirmation
- [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
- [ ] Complete example — the example is self-contained, including all data and the text of any traceback.
- [X] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
- [ ] New issue — a search of GitHub Issues suggests this is not a duplicate.
Relevant log output
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Input In [3], in <cell line: 1>()
----> 1 ds = xr.open_dataset("test.nc")
2 print(ds["temperature"].attrs)
3 ds.close()
File ~/.local/src/miniconda/envs/uptodatexarray/lib/python3.10/site-packages/xarray/backends/api.py:495, in open_dataset(filename_or_obj, engine, chunks, cache, decode_cf, mask_and_scale, decode_times, decode_timedelta, use_cftime, concat_characters, decode_coords, drop_variables, backend_kwargs, *args, **kwargs)
483 decoders = _resolve_decoders_kwargs(
484 decode_cf,
485 open_backend_dataset_parameters=backend.open_dataset_parameters,
(...)
491 decode_coords=decode_coords,
492 )
494 overwrite_encoded_chunks = kwargs.pop("overwrite_encoded_chunks", None)
--> 495 backend_ds = backend.open_dataset(
496 filename_or_obj,
497 drop_variables=drop_variables,
498 **decoders,
499 **kwargs,
500 )
501 ds = _dataset_from_backend_dataset(
502 backend_ds,
503 filename_or_obj,
(...)
510 **kwargs,
511 )
512 return ds
File ~/.local/src/miniconda/envs/uptodatexarray/lib/python3.10/site-packages/xarray/backends/netCDF4_.py:564, in NetCDF4BackendEntrypoint.open_dataset(self, filename_or_obj, mask_and_scale, decode_times, concat_characters, decode_coords, drop_variables, use_cftime, decode_timedelta, group, mode, format, clobber, diskless, persist, lock, autoclose)
562 store_entrypoint = StoreBackendEntrypoint()
563 with close_on_error(store):
--> 564 ds = store_entrypoint.open_dataset(
565 store,
566 mask_and_scale=mask_and_scale,
567 decode_times=decode_times,
568 concat_characters=concat_characters,
569 decode_coords=decode_coords,
570 drop_variables=drop_variables,
571 use_cftime=use_cftime,
572 decode_timedelta=decode_timedelta,
573 )
574 return ds
File ~/.local/src/miniconda/envs/uptodatexarray/lib/python3.10/site-packages/xarray/backends/store.py:27, in StoreBackendEntrypoint.open_dataset(self, store, mask_and_scale, decode_times, concat_characters, decode_coords, drop_variables, use_cftime, decode_timedelta)
24 vars, attrs = store.load()
25 encoding = store.get_encoding()
---> 27 vars, attrs, coord_names = conventions.decode_cf_variables(
28 vars,
29 attrs,
30 mask_and_scale=mask_and_scale,
31 decode_times=decode_times,
32 concat_characters=concat_characters,
33 decode_coords=decode_coords,
34 drop_variables=drop_variables,
35 use_cftime=use_cftime,
36 decode_timedelta=decode_timedelta,
37 )
39 ds = Dataset(vars, attrs=attrs)
40 ds = ds.set_coords(coord_names.intersection(vars))
File ~/.local/src/miniconda/envs/uptodatexarray/lib/python3.10/site-packages/xarray/conventions.py:503, in decode_cf_variables(variables, attributes, concat_characters, mask_and_scale, decode_times, decode_coords, drop_variables, use_cftime, decode_timedelta)
499 continue
500 stack_char_dim = (
501 concat_characters and v.dtype == "S1" and v.ndim > 0 and stackable(v.dims[-1])
502 )
--> 503 new_vars[k] = decode_cf_variable(
504 k,
505 v,
506 concat_characters=concat_characters,
507 mask_and_scale=mask_and_scale,
508 decode_times=decode_times,
509 stack_char_dim=stack_char_dim,
510 use_cftime=use_cftime,
511 decode_timedelta=decode_timedelta,
512 )
513 if decode_coords in [True, "coordinates", "all"]:
514 var_attrs = new_vars[k].attrs
File ~/.local/src/miniconda/envs/uptodatexarray/lib/python3.10/site-packages/xarray/conventions.py:354, in decode_cf_variable(name, var, concat_characters, mask_and_scale, decode_times, decode_endianness, stack_char_dim, use_cftime, decode_timedelta)
351 var = coder.decode(var, name=name)
353 if decode_timedelta:
--> 354 var = times.CFTimedeltaCoder().decode(var, name=name)
355 if decode_times:
356 var = times.CFDatetimeCoder(use_cftime=use_cftime).decode(var, name=name)
File ~/.local/src/miniconda/envs/uptodatexarray/lib/python3.10/site-packages/xarray/coding/times.py:537, in CFTimedeltaCoder.decode(self, variable, name)
534 def decode(self, variable, name=None):
535 dims, data, attrs, encoding = unpack_for_decoding(variable)
--> 537 if "units" in attrs and attrs["units"] in TIME_UNITS:
538 units = pop_to(attrs, encoding, "units")
539 transform = partial(decode_cf_timedelta, units=units)
TypeError: unhashable type: 'numpy.ndarray'
Anything else we need to know?
The following assignation produces the bug :
ds.temperature.attrs["units"] = []
But these ones does not produce the bug :
ds.temperature.attrs["units"] = "[]"
ds.temperature.attrs["units"] = ""
Also, i don't know how the units attributes get encoded for writing but i see no difference between ds.temperature.attrs["units"] = ""
and ds.temperature.attrs["units"] = []
when using ncdump
on the file
Environment
This bug was encountered with versions below this one.
INSTALLED VERSIONS
commit: None python: 3.10.4 (main, Mar 31 2022, 08:41:55) [GCC 7.5.0] python-bits: 64 OS: Linux OS-release: 5.13.0-52-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: fr_FR.UTF-8 LOCALE: ('fr_FR', 'UTF-8') libhdf5: 1.10.6 libnetcdf: 4.6.1
xarray: 0.20.1 pandas: 1.4.3 numpy: 1.22.3 scipy: None netCDF4: 1.5.7 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.5.1.1 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.5 dask: None distributed: None matplotlib: None cartopy: None seaborn: None numbagg: None fsspec: None cupy: None pint: None sparse: None setuptools: 61.2.0 pip: 22.1.2 conda: None pytest: None IPython: 8.4.0 sphinx: None
@antscloud As a workaround you could use keyword argument decode_cf=False
in the call to xr.open_dataset
. After fixing the units
attribute to some reasonable value you can call ds = xr.decode_cf(ds)
.
@antscloud As a workaround you could use keyword argument
decode_cf=False
in the call toxr.open_dataset
. After fixing theunits
attribute to some reasonable value you can callds = xr.decode_cf(ds)
.
Thank you, i'll do this. One could just loop over variables attributes and replace []
by an empty string in this particular case
I guess we could take a PR to change
if "units" in attrs and attrs["units"] in TIME_UNITS:
to
if "units" in attrs and isinstance(attrs["units"], str) and attrs["units"] in TIME_UNITS:
I was wondering why the units attribute is parsed this way in the first place ? It seems that this attribute is converted to a Python object (a list), is it xarray that does this or the binding of netcdf4 ?
If it's xarray, wouldn't it be better to just not parse it ?
It is checking to see if we can decode it as a time variable
I think this is now fixed by #7085 (thanks @ghislainp )