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
344631360,MDU6SXNzdWUzNDQ2MzEzNjA=,2315,Behavior of filter_by_attrs() does not match netCDF4.Dataset.get_variables_by_attributes,868027,closed,0,,,8,2018-07-25T22:35:14Z,2018-08-28T01:21:20Z,2018-08-28T01:21:20Z,CONTRIBUTOR,,,,"When using the `filter_by_attrs()` method of a Dataset it was returning more matches than I expected. The returned match set appears to be the logical OR of all the key=value pairs passed into the method. This does not match the behavior of the `netCDF4.Dataset.get_variables_by_attributes` which returns the logical AND of all the key=value pairs passed into it. I couldn't tell from the documentation if this was the intended behavior.

#### Minimal Example
```python
import xarray as xr
example_dataset = xr.Dataset({
    ""var1"": xr.DataArray([], attrs={""standard_name"": ""example1"", ""priority"": 0}),
    ""var2"": xr.DataArray([], attrs={""standard_name"": ""example2""})
})
example_dataset.filter_by_attrs(standard_name=""example2"", priority=0)
```

#### Example Output
```python
<xarray.Dataset>
Dimensions:  (dim_0: 0)
Dimensions without coordinates: dim_0
Data variables:
    var1     (dim_0) float64 
    var2     (dim_0) float64
```

#### Expected Output

```python
<xarray.Dataset>
Dimensions:  ()
Data variables:
    *empty*
```

Alternatively, chaining calls to filter_by_attrs will result in the expected behavior:
```python
import xarray as xr
example_dataset = xr.Dataset({
    ""var1"": xr.DataArray([], attrs={""standard_name"": ""example1"", ""priority"": 0}),
    ""var2"": xr.DataArray([], attrs={""standard_name"": ""example2""})
})
example_dataset.filter_by_attrs(standard_name=""example2"").filter_by_attrs(priority=0)

<xarray.Dataset>
Dimensions:  ()
Data variables:
    *empty*
```

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.0.final.0
python-bits: 64
OS: Darwin
OS-release: 17.7.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

xarray: 0.10.8
pandas: 0.23.3
numpy: 1.14.5
scipy: 1.1.0
netCDF4: 1.4.0
h5netcdf: None
h5py: None
Nio: None
zarr: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.18.2
distributed: 1.22.0
matplotlib: 2.2.2
cartopy: 0.16.0
seaborn: None
setuptools: 39.0.1
pip: 10.0.1
conda: None
pytest: 3.6.3
IPython: 6.4.0
sphinx: None

</details>
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