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/1952#issuecomment-370013168,https://api.github.com/repos/pydata/xarray/issues/1952,370013168,MDEyOklzc3VlQ29tbWVudDM3MDAxMzE2OA==,1217238,2018-03-02T18:38:28Z,2018-03-02T18:38:36Z,MEMBER,"I think that warning can be safely ignored in this case, but yes, that should also probably be silenced (see also https://github.com/pydata/xarray/issues/1652).","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,301795163
https://github.com/pydata/xarray/issues/1952#issuecomment-369978849,https://api.github.com/repos/pydata/xarray/issues/1952,369978849,MDEyOklzc3VlQ29tbWVudDM2OTk3ODg0OQ==,1217238,2018-03-02T16:46:34Z,2018-03-02T16:46:34Z,MEMBER,It looks like the simple fix is to reorder the check for timedelta64 in promote_dtype to be above the check for integer. Any interest in putting together a PR? :),"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,301795163
https://github.com/pydata/xarray/issues/1952#issuecomment-369974885,https://api.github.com/repos/pydata/xarray/issues/1952,369974885,MDEyOklzc3VlQ29tbWVudDM2OTk3NDg4NQ==,1217238,2018-03-02T16:34:07Z,2018-03-02T16:34:07Z,MEMBER,"Thanks for the clear report!

This seems to boil down to an issue with [`xarray.core.dtypes.promote_dtype`](https://github.com/pydata/xarray/blob/dc3eebf3a514cfdc1039b63f2a542121d1328ba9/xarray/core/dtypes.py#L68):
```
In [4]: from xarray.core import dtypes

In [5]: import numpy as np

In [7]: dtypes.maybe_promote(np.dtype('timedelta64[ns]'))
Out[7]: (dtype('float64'), nan)

In [9]: dtypes.maybe_promote(np.dtype('datetime64[ns]'))
Out[9]: (dtype('<M8[ns]'), numpy.datetime64('NaT'))
```

The source problem seems to be that numpy consider timedelta64 an integer subclass (?!?):
```
In [12]: issubclass(np.timedelta64, np.integer)
Out[12]: True
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,301795163