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
618985094,MDU6SXNzdWU2MTg5ODUwOTQ=,4065,keep_attrs not respected for unary operators,500246,closed,0,,,2,2020-05-15T13:55:14Z,2020-10-14T16:29:51Z,2020-10-14T16:29:51Z,CONTRIBUTOR,,,,"The xarray global option `keep_attrs` (introduced in #2482 ) is not respected for unary operators.

#### MCVE Code Sample

```python
import xarray as xr
x = xr.DataArray([1, 2, 3], attrs={""A"": ""B""})
with xr.set_options(keep_attrs=True):
    y = ~x
print(x.attrs, y.attrs)
```

#### Expected Output

I expect

```
{'A': 'B'} {'A': 'B'}
```

#### Problem Description

I get:

```
{'A': 'B'} {}
```

I get the same for the other unary operators `+x`, `-x`, and `abs(x)`.

#### Versions

Tested with latest xarray master (see below for details).

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

<!-- Paste the output here xr.show_versions() here -->
INSTALLED VERSIONS
------------------
commit: None
python: 3.8.2 | packaged by conda-forge | (default, Mar 23 2020, 18:16:37)
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 4.12.14-lp150.12.82-default
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
libhdf5: 1.10.5
libnetcdf: 4.7.4

xarray: 0.15.2.dev64+g2542a63f
pandas: 1.0.3
numpy: 1.18.1
scipy: 1.4.1
netCDF4: 1.5.3
pydap: None
h5netcdf: None
h5py: 2.10.0
Nio: None
zarr: 2.4.0
cftime: 1.1.1.2
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.3
cfgrib: None
iris: None
bottleneck: None
dask: 2.14.0
distributed: 2.14.0
matplotlib: 3.2.1
cartopy: 0.17.0
seaborn: None
numbagg: None
pint: None
setuptools: 46.1.3.post20200325
pip: 20.0.2
conda: installed
pytest: 5.4.1
IPython: 7.13.0
sphinx: None

</details>
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