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
289790965,MDU6SXNzdWUyODk3OTA5NjU=,1838,DataArray.sum does not respect dtype keyword,500246,closed,0,,,2,2018-01-18T22:01:07Z,2018-01-20T18:29:02Z,2018-01-20T18:29:02Z,CONTRIBUTOR,,,,"#### Code Sample, a copy-pastable example if possible

```python
# Your code here
da = xarray.DataArray(arange(5, dtype=""i2""))
print(da.sum(dtype=""i4"").dtype)
```
#### Problem description

The result is int64.  This is a problem because I asked for int32.

#### Expected Output

Expected output `int32`.

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

<details>
# Paste the output here xr.show_versions() here
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Linux
OS-release: 2.6.32-696.6.3.el6.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8

xarray: 0.10.0+dev12.gf882a58
pandas: 0.22.0
numpy: 1.14.0
scipy: 1.0.0
netCDF4: 1.3.1
h5netcdf: None
Nio: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.16.1
matplotlib: 2.1.1
cartopy: 0.15.1
seaborn: 0.8.1
setuptools: 38.4.0
pip: 9.0.1
conda: 4.3.16
pytest: 3.1.2
IPython: 6.1.0
sphinx: 1.6.2

</details>
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