issues: 297780998

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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
297780998 MDU6SXNzdWUyOTc3ODA5OTg= 1917 Decode times adds micro-second noise to standard calendar 145117 closed 0     5 2018-02-16T13:14:15Z 2018-02-26T10:28:17Z 2018-02-26T10:28:17Z CONTRIBUTOR      

Code Sample, a copy-pastable example if possible

I have a simplified NetCDF file with the following header:

```bash

netcdf foo { dimensions: time = UNLIMITED ; // (366 currently) x = 2 ; y = 2 ; variables: float time(time) ; time:standard_name = "time" ; time:long_name = "time" ; time:units = "DAYS since 2000-01-01 00:00:00" ; time:calendar = "standard" ; time:axis = "T" ; ... } ```

I would expect xarray to be able to decode these times. It does, but appears to do so incorrectly and without reporting any issues. Note the fractional time added to each date.

python In [4]: xr.open_dataset('foo.nc').time Out[4]: <xarray.DataArray 'time' (time: 366)> array(['2000-01-01T00:00:00.000000000', '2000-01-02T00:00:00.003211264', '2000-01-03T00:00:00.006422528', ..., '2000-12-29T00:00:01.962606592', '2000-12-30T00:00:01.672216576', '2000-12-31T00:00:01.381826560'], dtype='datetime64[ns]') Coordinates: * time (time) datetime64[ns] 2000-01-01 2000-01-02T00:00:00.003211264 ... Attributes: standard_name: time long_name: time axis: T

Problem description

Days since a valid date on a standard calendar should not add microseconds.

I know that xarray has time issues, for example #118 #521 numpy:#6207 #531 #789 and #848. But all of those appear to address non-standard times. This bug (if it is a bug) seems to occur with a very simple and straight forward calendar, and is silent, so it took me 2 days to figure out what was going on.

Output of xr.show_versions()

In [5]: xr.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 3.5.4.final.0 python-bits: 64 OS: Darwin OS-release: 16.7.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 xarray: 0.10.0 pandas: 0.22.0 numpy: 1.12.1 scipy: 0.19.1 netCDF4: 1.3.1 h5netcdf: None Nio: None bottleneck: 1.2.1 cyordereddict: 1.0.0 dask: 0.16.0 matplotlib: 2.1.1 cartopy: 0.15.1 seaborn: 0.8.1 setuptools: 38.4.0 pip: 9.0.1 conda: None pytest: None IPython: 6.2.1 sphinx: None 
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   completed 13221727 issue

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