html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/1008#issuecomment-248180310,https://api.github.com/repos/pydata/xarray/issues/1008,248180310,MDEyOklzc3VlQ29tbWVudDI0ODE4MDMxMA==,12339722,2016-09-20T01:53:43Z,2016-09-20T01:53:43Z,NONE,"OK & Thanks
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,177754433
https://github.com/pydata/xarray/issues/1008#issuecomment-248170532,https://api.github.com/repos/pydata/xarray/issues/1008,248170532,MDEyOklzc3VlQ29tbWVudDI0ODE3MDUzMg==,12339722,2016-09-20T00:44:27Z,2016-09-20T00:44:27Z,NONE,"Thanks for your reply.

**Variables dbz, vr and sw have the _FillValue attribute, whose value is equal to _FillValue: -999.0**

```
<type 'netCDF4._netCDF4.Variable'>
float32 dbz(z, y, x)
    _FillValue: -999.0
    units: dBZ
    long_name: reflectivity in log units
unlimited dimensions:
current shape = (9, 461, 461)
filling on
```

It seems that xarray will convert the dtype from float32 to float64, while the variable in netCDF4 file has the attribute `_FillValue`, `xr.open_dataset` auto identify the `_FillValue` in the variable and mask it with `np.nan` , however the variable is also changed into float64. I think this result with default argument is  not reasonable enough, as this type conversion is not necessary in fact.

Using `mask_and_scale=False` will maintain the variable in float32 and retain the `_FillValue` attribute of variable. However, what i want is mask but maintain the dtype in float32. Is it has possible bug in the internal of the `open_dataset` method ?
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,177754433