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1019478260,I_kwDOAMm_X848xAD0,5841,Dask error when importing pip installed xarray.,5669557,closed,0,,,12,2021-10-07T00:11:14Z,2021-12-03T12:33:59Z,2021-10-17T12:44:00Z,NONE,,,,"<!-- Please include a self-contained copy-pastable example that generates the issue if possible.

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**What happened**:

I am pip installing `xarray` version 0.19.0 on python 3.9.7 and am getting the following error when trying to `import xarray`

```
    import xarray as xr
/usr/local/lib/python3.9/site-packages/xarray/__init__.py:3: in <module>
    from . import testing, tutorial, ufuncs
/usr/local/lib/python3.9/site-packages/xarray/testing.py:8: in <module>
    from xarray.core import duck_array_ops, formatting, utils
/usr/local/lib/python3.9/site-packages/xarray/core/duck_array_ops.py:15: in <module>
    from . import dask_array_compat, dask_array_ops, dtypes, npcompat, nputils
/usr/local/lib/python3.9/site-packages/xarray/core/dask_array_compat.py:5: in <module>
    from .pycompat import dask_version
/usr/local/lib/python3.9/site-packages/xarray/core/pycompat.py:55: in <module>
    dsk = DuckArrayModule(""dask"")
/usr/local/lib/python3.9/site-packages/xarray/core/pycompat.py:22: in __init__
    duck_array_version = LooseVersion(duck_array_module.__version__)
E   AttributeError: module 'dask' has no attribute '__version__'

```

**What you expected to happen**:

Doing `pip install ""xarray[complete]""` fixes the issue.
However, I don't want to install dask or the other optional packages as I want to reduce dependencies in my project.

**Minimal Complete Verifiable Example**:

```python
import xarray  as xr # :)
```

**Anything else we need to know?**:

Thanks

**Environment**:

NA
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