issue_comments: 566214653

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https://github.com/pydata/xarray/issues/3470#issuecomment-566214653 https://api.github.com/repos/pydata/xarray/issues/3470 566214653 MDEyOklzc3VlQ29tbWVudDU2NjIxNDY1Mw== 1217238 2019-12-16T19:48:38Z 2019-12-16T19:48:38Z MEMBER

The main problem is that when you write ds.time.values = something, you are modifying an attribute of a DataArray that happens to use the same variable as the as the Dataset, but otherwise the DataArray and Dataset are entirely independent. The DataArray does not have a reference to the original dataset, so it can't check or update the indexes.

This happened to work in previous versions of xarray, but only because indexes always mapped directly into the data of an xarray.Variable. But I don't think this is the right pattern to continue in the future, especially because we want to do define indexes over multiple variables (e.g., for MultiIndex).

I think what we probably want to do is mark variables used in indexes as having immutable data in xarray's data model, and raise an error for attempts to modify them in-place.

 
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