pull_requests: 657205536

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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
657205536 MDExOlB1bGxSZXF1ZXN0NjU3MjA1NTM2 5402 open 0 `dt.to_pytimedelta` to allow arithmetic with cftime objects 20629530 <!-- Feel free to remove check-list items aren't relevant to your change --> - [ ] Closes #xxxx - [x] Tests added - [x] Passes `pre-commit run --all-files` - [ ] User visible changes (including notable bug fixes) are documented in `whats-new.rst` - [ ] New functions/methods are listed in `api.rst` When playing with cftime objects a problem I encountered many times is that I can sub two arrays and them add it back to another. Subtracting to cftime datetime arrays result in an array of `np.timedelta64`. And when trying to add it back to another cftime array, we get a `UFuncTypeError` because the two arrays have incompatible dtypes : '<m8[ns]' and 'O'. Example: ```python import xarray as xr da = xr.DataArray(xr.cftime_range('1900-01-01', freq='D', periods=10), dims=('time',)) # An array of timedelta64[ns] dt = da - da[0] da[-1] + dt # Fails ``` However, if the two arrays were of 'O' dtype, then the subtraction would be made by `cftime` which supports `datetime.timedelta` objects. This solution here adds a `to_pytimedelta` to the `TimedeltaAccessor`, mirroring the name of the similar function on `pd.Series.dt`. It uses a monkeypatching workaround to prevent xarray to case the array back into numpy objects. The user still has to check if the data is in cftime or numpy to adapt the operation (calling `dt.to_pytimedelta` or not), but custom workaround were always overly complicated for such a simple problem, this helps. Also, this doesn't work with dask arrays because loading a dask array triggers the variable constructor and thus recasts the array of `datetime.timedelta` to `numpy.timedelta[64]`. I realize I maybe should have opened an issue before, but I had this idea and it all rushed along. 2021-05-28T22:48:50Z 2022-06-09T14:50:16Z     0060277e4ecf1b05a198aeff9051d86f814b0096     0 71d567789573b47e059dbaebabcbda9c3493d0c5 d1e4164f3961d7bbb3eb79037e96cae14f7182f8 CONTRIBUTOR   13221727 https://github.com/pydata/xarray/pull/5402  

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