issues

What happened?

Saving and loading from netcdf with engine=scipy produces an unexpected valueerror on read. The file seems to be corrupted.

What did you expect to happen?

reading works just fine.

Minimal Complete Verifiable Example

```Python import numpy as np import xarray as xr ds = xr.Dataset( { "values": ( ["name", "time"], np.array([[]], dtype=np.float32).T, ) }, coords={"time": [1], "name": []}, ).expand_dims({"index": [0]})

ds.to_netcdf("file.nc", engine="scipy") _ = xr.open_dataset("file.nc", engine="scipy")

```

MVCE confirmation

• [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• [X] 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.
• [X] New issue — a search of GitHub Issues suggests this is not a duplicate.
• [X] Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

```Python KeyError Traceback (most recent call last) File .../python3.11/site-packages/xarray/backends/file_manag er.py:211, in CachingFileManager._acquire_with_cache_info(self, needs_lock) 210 try: --> 211 file = self._cache[self._key] 212 except KeyError:

File .../python3.11/site-packages/xarray/backends/lru_cache. py:56, in LRUCache.getitem(self, key) 55 with self._lock: ---> 56 value = self._cache[key] 57 self._cache.move_to_end(key)

KeyError: [<function _open_scipy_netcdf at 0x7fe96afa9120>, ('/home/eivind/Projects/ert/file.nc',), 'r', (('mmap', None), ('version', 2)), '264ec6b3-78b3-4766-bb41-7656d6a51962']

During handling of the above exception, another exception occurred:

TypeError Traceback (most recent call last) Cell In[1], line 18 4 ds = ( 5 xr.Dataset( 6 { (...) 15 .expand_dims({"index": [0]}) 16 ) 17 ds.to_netcdf("file.nc", engine="scipy") ---> 18 _ = xr.open_dataset("file.nc", engine="scipy")

File .../python3.11/site-packages/xarray/backends/api.py:572 , in open_dataset(filename_or_obj, engine, chunks, cache, decode_cf, mask_and_scale, decode_times, d ecode_timedelta, use_cftime, concat_characters, decode_coords, drop_variables, inline_array, chunked _array_type, from_array_kwargs, backend_kwargs, kwargs) 560 decoders = _resolve_decoders_kwargs( 561 decode_cf, 562 open_backend_dataset_parameters=backend.open_dataset_parameters, (...) 568 decode_coords=decode_coords, 569 ) 571 overwrite_encoded_chunks = kwargs.pop("overwrite_encoded_chunks", None) --> 572 backend_ds = backend.open_dataset( 573 filename_or_obj, 574 drop_variables=drop_variables, 575 decoders, 576 kwargs, 577 ) 578 ds = _dataset_from_backend_dataset( 579 backend_ds, 580 filename_or_obj, (...) 590 kwargs, 591 ) 592 return ds

File .../python3.11/site-packages/xarray/backends/scipy_.py: 315, in ScipyBackendEntrypoint.open_dataset(self, filename_or_obj, mask_and_scale, decode_times, con cat_characters, decode_coords, drop_variables, use_cftime, decode_timedelta, mode, format, group, mm ap, lock) 313 store_entrypoint = StoreBackendEntrypoint() 314 with close_on_error(store): --> 315 ds = store_entrypoint.open_dataset( 316 store, 317 mask_and_scale=mask_and_scale, 318 decode_times=decode_times, 319 concat_characters=concat_characters, 320 decode_coords=decode_coords, 321 drop_variables=drop_variables, 322 use_cftime=use_cftime, 323 decode_timedelta=decode_timedelta, 324 ) 325 return ds

File .../python3.11/site-packages/xarray/backends/store.py:4 3, in StoreBackendEntrypoint.open_dataset(self, filename_or_obj, mask_and_scale, decode_times, conca t_characters, decode_coords, drop_variables, use_cftime, decode_timedelta) 29 def open_dataset( # type: ignore[override] # allow LSP violation, not supporting **kwargs 30 self, 31 filename_or_obj: str | os.PathLike[Any] | BufferedIOBase | AbstractDataStore, (...) 39 decode_timedelta=None, 40 ) -> Dataset: 41 assert isinstance(filename_or_obj, AbstractDataStore) ---> 43 vars, attrs = filename_or_obj.load() 44 encoding = filename_or_obj.get_encoding() 46 vars, attrs, coord_names = conventions.decode_cf_variables( 47 vars, 48 attrs, (...) 55 decode_timedelta=decode_timedelta, 56 )

File .../python3.11/site-packages/xarray/backends/common.py: 210, in AbstractDataStore.load(self) 188 def load(self): 189 """ 190 This loads the variables and attributes simultaneously. 191 A centralized loading function makes it easier to create (...) 207 are requested, so care should be taken to make sure its fast. 208 """ 209 variables = FrozenDict( --> 210 (_decode_variable_name(k), v) for k, v in self.get_variables().items() 211 ) 212 attributes = FrozenDict(self.get_attrs()) 213 return variables, attributes

File .../python3.11/site-packages/xarray/backends/scipy_.py: 181, in ScipyDataStore.get_variables(self) 179 def get_variables(self): 180 return FrozenDict( --> 181 (k, self.open_store_variable(k, v)) for k, v in self.ds.variables.items() 182 )

File .../python3.11/site-packages/xarray/backends/scipy_.py: 170, in ScipyDataStore.ds(self) 168 @property 169 def ds(self): --> 170 return self._manager.acquire()

File .../python3.11/site-packages/xarray/backends/file_manag er.py:193, in CachingFileManager.acquire(self, needs_lock) 178 def acquire(self, needs_lock=True): 179 """Acquire a file object from the manager. 180 181 A new file is only opened if it has expired from the (...) 191 An open file object, as returned by opener(*args, **kwargs). 192 """ --> 193 file, _ = self._acquire_with_cache_info(needs_lock) 194 return file

File .../python3.11/site-packages/xarray/backends/file_manag er.py:217, in CachingFileManager._acquire_with_cache_info(self, needs_lock) 215 kwargs = kwargs.copy() 216 kwargs["mode"] = self._mode --> 217 file = self._opener(self._args, *kwargs) 218 if self._mode == "w": 219 # ensure file doesn't get overridden when opened again 220 self._mode = "a"

File .../python3.11/site-packages/xarray/backends/scipy_.py: 109, in _open_scipy_netcdf(filename, mode, mmap, version) 106 filename = io.BytesIO(filename) 108 try: --> 109 return scipy.io.netcdf_file(filename, mode=mode, mmap=mmap, version=version) 110 except TypeError as e: # netcdf3 message is obscure in this case 111 errmsg = e.args[0]

File .../python3.11/site-packages/scipy/io/_netcdf.py:278, i n netcdf_file.init(self, filename, mode, mmap, version, maskandscale) 275 self._attributes = {} 277 if mode in 'ra': --> 278 self._read()

File .../python3.11/site-packages/scipy/io/_netcdf.py:607, i n netcdf_file._read(self) 605 self._read_dim_array() 606 self._read_gatt_array() --> 607 self._read_var_array()

File .../python3.11/site-packages/scipy/io/netcdf.py:688, i n netcdf_file._read_var_array(self) 685 data = None 686 else: # not a record variable 687 # Calculate size to avoid problems with vsize (above) --> 688 a_size = reduce(mul, shape, 1) * size 689 if self.use_mmap: 690 data = self._mm_buf[begin:begin_+a_size].view(dtype=dtype_)

TypeError: unsupported operand type(s) for *: 'int' and 'NoneType' ```

Anything else we need to know?

No response

Environment