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
1773886549,I_kwDOAMm_X85pu1xV,7942,Numpy raises warning in `xarray.coding.times.cast_to_int_if_safe`,132147,closed,0,,,2,2023-06-26T05:03:46Z,2023-09-17T08:15:27Z,2023-09-17T08:15:27Z,CONTRIBUTOR,,,,"### What happened?

In recent versions of numpy, calling `numpy.asarray(arr, dtype=numpy.int64)` will raise a warning if the input array contains `numpy.nan` values. This line of code is used in `xarray.coding.times.cast_to_int_if_safe(num)`:

```python
def cast_to_int_if_safe(num) -> np.ndarray:
    int_num = np.asarray(num, dtype=np.int64)
    if (num == int_num).all():
        num = int_num
    return num
```

The function still returns the correct True/False values regardless of the warning.

### What did you expect to happen?

No warning to be printed

### Minimal Complete Verifiable Example

```Python
import numpy
import xarray

one_day = numpy.timedelta64(1, 'D')
nat = numpy.timedelta64('nat')

timedelta_values = (numpy.arange(5) * one_day).astype('timedelta64[ns]')
timedelta_values[2] = nat
timedelta_values[4] = nat

dataset = xarray.Dataset(data_vars={
    'timedeltas': xarray.DataArray(data=timedelta_values, dims=['x'])
})
dataset.to_netcdf('out.nc')
```


### MVCE confirmation

- [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
- [X] Complete example — the example is self-contained, including all data and the text of any traceback.
- [X] Verifiable example — the example copy & pastes into an IPython prompt or [Binder notebook](https://mybinder.org/v2/gh/pydata/xarray/main?urlpath=lab/tree/doc/examples/blank_template.ipynb), returning the result.
- [X] New issue — a search of GitHub Issues suggests this is not a duplicate.

### Relevant log output

```Python
$ python3 safe_cast.py
/home/hea211/projects/emsarray/.conda/lib/python3.10/site-packages/xarray/coding/times.py:618: RuntimeWarning: invalid value encountered in cast
  int_num = np.asarray(num, dtype=np.int64)

$ ncdump out.nc
netcdf out {
dimensions:
        x = 5 ;
variables:
        double timedeltas(x) ;
                timedeltas:_FillValue = NaN ;
                timedeltas:units = ""days"" ;
data:

 timedeltas = 0, 1, _, 3, _ ;
}
```


### Anything else we need to know?

I saw the `numpy.can_cast` function and tried to use that to solve the issue (see PR #7834), however this function did not do what I expected it to.

A search for other solutions to see whether an array of floating point values is representable as integers turned up [Numpy: Check if float array contains whole numbers](https://stackoverflow.com/questions/35042128/numpy-check-if-float-array-contains-whole-numbers) on Stack Overflow. There are a few solutions given in that question, although each has its drawbacks. The most complete solution appears to be [is_integer_ufunc](https://gitlab.com/madphysicist/is_integer_ufunc), which is a ufunc written in C. Unfortunately this is not installable via pip/conda, and is not included in numpy.

### Environment

<details>

In [2]: import xarray as xr
   ...: xr.show_versions()
/home/hea211/projects/emsarray/.conda/lib/python3.10/site-packages/_distutils_hack/__init__.py:33: UserWarning: Setuptools is replacing distutils.
  warnings.warn(""Setuptools is replacing distutils."")

INSTALLED VERSIONS
------------------
commit: None
python: 3.10.0 (default, Mar  3 2022, 09:58:08) [GCC 7.5.0]
python-bits: 64
OS: Linux
OS-release: 5.15.0-73-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_AU.UTF-8
LOCALE: ('en_AU', 'UTF-8')
libhdf5: 1.12.2
libnetcdf: 4.9.1

xarray: 2023.4.2
pandas: 2.0.1
numpy: 1.24.3
scipy: None
netCDF4: 1.6.3
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.2
nc_time_axis: None
PseudoNetCDF: None
iris: None
bottleneck: 1.3.7
dask: 2023.4.1
distributed: 2023.4.1
matplotlib: 3.7.1
cartopy: 0.21.1
seaborn: None
numbagg: None
fsspec: 2023.5.0
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: 65.6.3
pip: 22.3.1
conda: None
pytest: 7.3.1
mypy: 1.3.0
IPython: 8.12.0
sphinx: 4.3.2


</details>
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/7942/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue
1705163672,PR_kwDOAMm_X85QQiiY,7834,Use `numpy.can_cast` instead of casting and checking,132147,closed,0,,,5,2023-05-11T06:36:06Z,2023-06-26T05:06:30Z,2023-06-26T05:06:29Z,CONTRIBUTOR,,1,pydata/xarray/pulls/7834,"In numpy >= 1.24 unsafe casting raises a RuntimeWarning for an operation that xarray does often to check if casting is safe. `numpy.can_cast` looks like an alternative approach designed for this exact case.

<!-- Feel free to remove check-list items aren't relevant to your change -->

- [ ] Tests added
- [x] User visible changes (including notable bug fixes) are documented in `whats-new.rst`
- [ ] New functions/methods are listed in `api.rst`
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/7834/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
1596115847,I_kwDOAMm_X85fIsuH,7549,HDF5-DIAG warnings calling `open_mfdataset` with more than `file_cache_maxsize` datasets (hdf5 1.12.2),132147,open,0,,,10,2023-02-23T02:28:23Z,2023-03-26T00:41:11Z,,CONTRIBUTOR,,,,"### What happened?

Using `ds = open_mfdataset(...)` to open more than `file_cache_maxsize` files, then saving the combined dataset with `ds.to_netcdf()` prints many HDF5-DIAG warnings. This happens when using `hdf5==1.12.2` as bundled with `netcdf4~=1.6.0`. Downgrading to `netcdf4~=1.5.8` which bundles `hdf5==1.12.0` stops the warnings being printed. The output file appears to be correct in either case.

### What did you expect to happen?

No warnings from HDF5-DIAG. Either raise an error because of the number of files being opened at once, or behaving as `open_mfdataset()` normally does.

### Minimal Complete Verifiable Example

```Python
import argparse
import pathlib
import tempfile
from typing import List

import netCDF4
import xarray

HERE = pathlib.Path(__file__).parent


def add_arguments(parser: argparse.ArgumentParser):
    parser.add_argument('count', type=int, default=200, nargs='?')
    parser.add_argument('--file-cache-maxsize', type=int, required=False)


def main():
    parser = argparse.ArgumentParser()
    add_arguments(parser)
    opts = parser.parse_args()

    if opts.file_cache_maxsize is not None:
        xarray.set_options(file_cache_maxsize=opts.file_cache_maxsize)

    temp_dir = tempfile.mkdtemp(dir=HERE, prefix='work-dir-')
    work_dir = pathlib.Path(temp_dir)
    print(""Working in"", work_dir.name)

    print(""Making"", opts.count, ""datasets"")
    dataset_paths = make_many_datasets(work_dir, count=opts.count)

    print(""Combining"", len(dataset_paths), ""datasets"")
    dataset = xarray.open_mfdataset(dataset_paths, lock=False)
    dataset.to_netcdf(work_dir / 'combined.nc')


def make_many_datasets(
    work_dir: pathlib.Path,
    count: int = 200
) -> List[pathlib.Path]:
    dataset_paths = []
    for i in range(count):
        variable = f'var_{i}'
        path = work_dir / f'{variable}.nc'
        dataset_paths.append(path)
        make_dataset(path, variable)

    return dataset_paths


def make_dataset(
    path: pathlib.Path,
    variable: str,
) -> None:
    ds = netCDF4.Dataset(path, ""w"", format=""NETCDF4"")
    ds.createDimension(""x"", 1)
    var = ds.createVariable(variable, ""i8"", (""x"",))
    var[:] = 1
    ds.close()


if __name__ == '__main__':
    main()
```


### MVCE confirmation

- [x] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
- [x] Complete example — the example is self-contained, including all data and the text of any traceback.
- [x] Verifiable example — the example copy & pastes into an IPython prompt or [Binder notebook](https://mybinder.org/v2/gh/pydata/xarray/main?urlpath=lab/tree/doc/examples/blank_template.ipynb), returning the result.
- [x] New issue — a search of GitHub Issues suggests this is not a duplicate.

### Relevant log output

```Python
Working in work-dir-yi3jp5ly
Making 128 datasets
Combining 128 datasets
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 1:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitGroomNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 1:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeGranularBitRoundNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 1:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitRoundNumberOfSignificantBits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 1:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitGroomNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 1:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeGranularBitRoundNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 1:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitRoundNumberOfSignificantBits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 2:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitGroomNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 2:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeGranularBitRoundNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 2:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitRoundNumberOfSignificantBits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 3:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitGroomNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 3:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeGranularBitRoundNumberOfSignificantDigits'
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.12.2) thread 3:
  #000: H5A.c line 528 in H5Aopen_by_name(): can't open attribute
    major: Attribute
    minor: Can't open object
  #001: H5VLcallback.c line 1091 in H5VL_attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #002: H5VLcallback.c line 1058 in H5VL__attr_open(): attribute open failed
    major: Virtual Object Layer
    minor: Can't open object
  #003: H5VLnative_attr.c line 130 in H5VL__native_attr_open(): can't open attribute
    major: Attribute
    minor: Can't open object
  #004: H5Aint.c line 545 in H5A__open_by_name(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #005: H5Oattribute.c line 494 in H5O__attr_open_by_name(): can't locate attribute: '_QuantizeBitRoundNumberOfSignificantBits'
    major: Attribute
    minor: Object not found
```


### Anything else we need to know?

The example is a script to run on the command line. Assuming the file is named `test.py`, invoke as:

```shell
# This will show the error. Defaults to making 200 files
$ python3 ./test.py
# This will not show the error - the number of files is less than file_cache_maxsize:
$ python3 ./test.py 127
# This will adjust file_cache_maxsize to show the error again, despite the lower number of files
$ python3 ./test.py 11 --file-cache-maxsize=10
```

The log output is from `python3 ./test.py 128`. The length of the log output depends on the number of files opened - the more files the longer the log. The log output from `python3 ./test.py` using the default of 200 datasets was too long to include in this issue!

All output files are restricted to directories created in the current working directory named `work-dir-XXXXXXX`, and are retained after the program exits. 200 datasets take up a total of 1.7MB.

### Environment

Failing environment:
<details>


INSTALLED VERSIONS
------------------
commit: None
python: 3.8.10 (default, Nov 14 2022, 12:59:47) 
[GCC 9.4.0]
python-bits: 64
OS: Linux
OS-release: 5.15.0-58-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_AU.UTF-8
LOCALE: ('en_AU', 'UTF-8')
libhdf5: 1.12.2
libnetcdf: 4.9.0

xarray: 2023.1.0
pandas: 1.5.3
numpy: 1.24.2
scipy: None
netCDF4: 1.6.2
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.2
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2023.2.0
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
fsspec: 2023.1.0
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: 44.0.0
pip: 23.0.1
conda: None
pytest: None
mypy: None
IPython: None
sphinx: None


</details>

Working environment:
<details>


INSTALLED VERSIONS
------------------
commit: None
python: 3.8.10 (default, Nov 14 2022, 12:59:47) 
[GCC 9.4.0]
python-bits: 64
OS: Linux
OS-release: 5.15.0-58-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_AU.UTF-8
LOCALE: ('en_AU', 'UTF-8')
libhdf5: 1.12.0
libnetcdf: 4.7.4

xarray: 2023.1.0
pandas: 1.5.3
numpy: 1.24.2
scipy: None
netCDF4: 1.5.8
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.2
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2023.2.0
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
fsspec: 2023.1.0
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: 44.0.0
pip: 23.0.1
conda: None
pytest: None
mypy: None
IPython: None
sphinx: None


</details>","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/7549/reactions"", ""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,issue
1071806607,PR_kwDOAMm_X84va6lN,6049,Attempt datetime coding using cftime when pandas fails,132147,closed,0,,,2,2021-12-06T07:12:35Z,2022-01-04T00:28:15Z,2021-12-24T11:48:22Z,CONTRIBUTOR,,0,pydata/xarray/pulls/6049,"A netCDF4 dataset we use has a time variable defined as:
```
        double time(time) ;
                time:axis = ""T"" ;
                time:bounds = ""time_bnds"" ;
                time:calendar = ""gregorian"" ;
                time:long_name = ""time"" ;
                time:standard_name = ""time"" ;
                time:units = ""days since 1970-01-01 00:00:00 00"" ;
```

Note the `units` attribute, specifically a timezone offset of `00` without any `+-` sign.

xarray can successfully open this dataset and parse the time units, making a time variable with the expeced values. However, attempting to save this dataset (e.g. after slicing some geographic bounds or selecting a subset of variables), xarray would raise an error trying to reformat the time `units`.

This fix applies the same logic used in the decoding step to the encoding step - specifically, attempt to use `pandas` but if that fails then use `cftime`. The decoding step catches `ValueError` to do this, but `ValueError` was not caught in the encode workflow.

- [x] Tests added
- [x] Passes `pre-commit run --all-files`
- [x] User visible changes (including notable bug fixes) are documented in `whats-new.rst`","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6049/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull