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
313010564,MDU6SXNzdWUzMTMwMTA1NjQ=,2049,Keeping attributes when using DataArray.astype,4180033,closed,0,,,5,2018-04-10T17:02:18Z,2020-08-19T20:34:35Z,2020-08-19T20:34:35Z,NONE,,,,"Hi all,

I was wondering whether there is an easier way to keep the attributes when using the DataArray.astype method?

```python
import xarray as xr

# DataArray with attributes
da = xr.DataArray(
    [[0, 1, 2], [0, 1, 2]], attrs={""attr1"": ""value1""}
)

# the attributes are not passed over to new_da
new_da = da.astype(float)
# I have to set the attributes by myself
new_da.attrs = da.attrs.copy()
```

This is just one extra-line, but I have to keep track of the old DataArray and it may become unhandy if I do many astype calls.

Any hints?

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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.4.final.0
python-bits: 64
OS: Linux
OS-release: 3.16.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.utf8
LOCALE: en_US.UTF-8

xarray: 0.10.2
pandas: 0.22.0
numpy: 1.14.2
scipy: 1.0.0
netCDF4: 1.3.1
h5netcdf: 0.5.0
h5py: 2.7.1
Nio: None
zarr: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.17.2
distributed: 1.21.4
matplotlib: 2.2.2
cartopy: 0.16.0
seaborn: 0.8.1
setuptools: 39.0.1
pip: 9.0.1
conda: None
pytest: 3.4.2
IPython: 6.2.1
sphinx: 1.7.1
</details>
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316726712,MDU6SXNzdWUzMTY3MjY3MTI=,2076,Get sub level names from multiindex,4180033,closed,0,,,2,2018-04-23T09:14:30Z,2018-05-18T05:13:38Z,2018-05-18T05:13:38Z,NONE,,,,"Hi,
is there any method / attribute to get the sub level names from a MultiIndex?

```python
ds = xr.Dataset({
    ""lat"": np.arange(100),
    ""lon"": np.arange(100),
})
ds.stack(main=(""lat"", ""lon""))
```

```
<xarray.Dataset>
Dimensions:  (main: 10000)
Coordinates:
  * main     (main) MultiIndex
  - lat      (main) int64 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ...
  - lon      (main) int64 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 ...
Data variables:
    *empty*
```

I would like to have the names `lat` and `lon` as a list (let's assume I did not know that they were stacked together). They should be stored internally, right? I even went through the formatting module to search for the correct attribute but I could not find it.

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

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Linux
OS-release: 3.16.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.utf8
LOCALE: en_US.UTF-8

xarray: 0.10.3
pandas: 0.22.0
numpy: 1.14.2
scipy: 1.0.1
netCDF4: 1.3.1
h5netcdf: 0.5.0
h5py: 2.7.1
Nio: None
zarr: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.17.2
distributed: 1.21.6
matplotlib: 2.2.2
cartopy: 0.16.0
seaborn: 0.8.1
setuptools: 39.0.1
pip: 9.0.3
conda: None
pytest: 3.5.0
IPython: 6.3.1
sphinx: 1.7.2
</details>
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