id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
550067372,MDU6SXNzdWU1NTAwNjczNzI=,3696,AttributeError: cannot set attribute '_accessors' on a 'DataArray' object.,8020943,closed,0,,,6,2020-01-15T09:31:18Z,2020-01-16T12:09:52Z,2020-01-15T15:18:05Z,NONE,,,,"#### MCVE Code Sample

Create two `conda` environments:
- `conda create --name xr140 python xarray==0.14.0 ipython -y`
- `conda create --name xr141 python xarray==0.14.1 ipython -y`

The following works if you run all of it within the same environment. However, if you store it with `xarray=0.14.0`, and load it with `xarray=0.14.1`, then it fails.

```python
import shelve
import xarray as xr
import numpy as np

data = xr.DataArray(data=np.arange(10), dims=[""test""])

# Store data
with shelve.open('test') as db:
    db['data'] = data

# Load data
with shelve.open('test') as db:
    newdata = db['data']

np.allclose(data, newdata)
```

#### Expected Output

One should be able to load the pickle no matter what the version of `xarray` is.

#### Problem Description

Storing with `xarray=0.14.0` and trying to load with `xarray=0.14.1` results in the following output:
```
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
~/anaconda3/envs/xarray141/lib/python3.8/shelve.py in __getitem__(self, key)
    110         try:
--> 111             value = self.cache[key]
    112         except KeyError:

KeyError: 'data'

During handling of the above exception, another exception occurred:

AttributeError                            Traceback (most recent call last)
~/anaconda3/envs/xarray141/lib/python3.8/site-packages/xarray/core/common.py in __setattr__(self, name, value)
    261         try:
--> 262             object.__setattr__(self, name, value)
    263         except AttributeError as e:

AttributeError: 'DataArray' object has no attribute '_accessors'

The above exception was the direct cause of the following exception:

AttributeError                            Traceback (most recent call last)
<ipython-input-1-f8dc3ae27b24> in <module>
      5 # Load data
      6 with shelve.open('test') as db:
----> 7     newdata = db['data']
      8 

~/anaconda3/envs/xarray141/lib/python3.8/shelve.py in __getitem__(self, key)
    112         except KeyError:
    113             f = BytesIO(self.dict[key.encode(self.keyencoding)])
--> 114             value = Unpickler(f).load()
    115             if self.writeback:
    116                 self.cache[key] = value

~/anaconda3/envs/xarray141/lib/python3.8/site-packages/xarray/core/common.py in __setattr__(self, name, value)
    268             ):
    269                 raise
--> 270             raise AttributeError(
    271                 ""cannot set attribute %r on a %r object. Use __setitem__ style""
    272                 ""assignment (e.g., `ds['name'] = ...`) instead of assigning variables.""

AttributeError: cannot set attribute '_accessors' on a 'DataArray' object. Use __setitem__ styleassignment (e.g., `ds['name'] = ...`) instead of assigning variables.
```


#### Output of ``xr.show_versions()``

The `xr.show_versions()` for the two environments are identical, except for the `xarray` versions.
<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.8.1 (default, Jan  8 2020, 22:29:32) 
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 4.15.0-74-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
libhdf5: None
libnetcdf: None

xarray: 0.14.0 OR 0.14.1
pandas: 0.25.3
numpy: 1.17.4
scipy: None
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
setuptools: 44.0.0.post20200106
pip: 19.3.1
conda: None
pytest: None
IPython: 7.11.1
sphinx: None
</details>
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