issue_comments: 459177873

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https://github.com/pydata/xarray/pull/2706#issuecomment-459177873 https://api.github.com/repos/pydata/xarray/issues/2706 459177873 MDEyOklzc3VlQ29tbWVudDQ1OTE3Nzg3Mw== 1197350 2019-01-31T01:24:11Z 2019-01-31T01:24:11Z MEMBER

So the problem in @davidbrochart's example is that there are different encodings on the time variables in the two datasets.

When writing datetimes, xarray automatically picks an encoding (i.e. days since 2000-01-01 00:00:00) based on some heuristics. When serializing the dataset, this encoding is used to encode the datetime64[ns] dtype into a different dtype, and the encoding is placed in the attributes of the store. When you open the dataset, the encoding is automatically decoded according to CF conventions. This can be disabled by using decode_cf=False or decode_times=False when you open the dataset.

In this case, xarray's heuristics are picking different encodings for the two dates. You could make this example work by manually specifying encoding on the appended dataset to be the same as the original.

This example illustrates the need for some sort of compatibility checks between the target dataset and the appended dataset. For example, checking for attribute compatibility would have caught this error.

 
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