pull_requests: 1088466399

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id node_id number state locked title user body created_at updated_at closed_at merged_at merge_commit_sha assignee milestone draft head base author_association auto_merge repo url merged_by
1088466399 PR_kwDOAMm_X85A4K3f 7171 closed 0 Set `longdouble=False` in `cftime.date2num` within the date encoding context 6628425 Currently, the default behavior of `cftime.date2num` is to return integer values when possible (i.e. when the encoding units allow), and fall back to returning float64 values when that is not possible. Recently, [cftime added the option to use float128 as the fallback dtype](https://github.com/Unidata/cftime/pull/284#issuecomment-1176098280), which enables greater potential roundtrip precision. This is through the `longdouble` flag to `cftime.date2num`, which currently defaults to `False`. It was intentionally set to `False` by default, because netCDF does not support storing float128 values in files, and so, without any changes, would otherwise break xarray's encoding procedure. The desire in cftime, however, is to eventually set this flag to `True` by default (https://github.com/Unidata/cftime/issues/297). This PR makes the necessary changes in xarray to adapt to this eventual new default. Essentially if the `longdouble` argument is allowed in the user's version of `cftime.date2num`, we explicitly set it to `False` to preserve the current float64 fallback behavior within the context of encoding times. There are a few more places where `date2num` is used (some additional places in the tests, and [in `calendar_ops.py`](https://github.com/pydata/xarray/blob/93f1ba226086d5a916f54653e870a2943fe09ab7/xarray/coding/calendar_ops.py#L277)), but in those places using float128 values would not present a problem. At some point we might consider relaxing this behavior in xarray, since it is possible to store float128 values in zarr stores for example, but for the time being the simplest approach seems to be to stick with float64 for all backends (it would be complicated to have backend-specific defaults). cc: @jswhit 2022-10-16T18:20:58Z 2022-10-18T16:38:24Z 2022-10-18T16:37:57Z 2022-10-18T16:37:57Z 9df2dfca57e1c672f6faf0f7945d2f38921a4bb2     0 05853187cc1bb1d25cecad6c7de9c633a3ac4ec8 93f1ba226086d5a916f54653e870a2943fe09ab7 MEMBER   13221727 https://github.com/pydata/xarray/pull/7171  

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