What is your issue?

Recent changes in Dask's tokenization process (https://github.com/dask/dask/pull/10876) seem to have introduced unexpected behavior in Xarray's test suite. This has led to CI failures, specifically in tests related to tokenization.

• https://github.com/pydata/xarray/actions/runs/8069874717/job/22045898877

```python ---------- coverage: platform linux, python 3.12.2-final-0 ----------- Coverage XML written to file coverage.xml

=========================== short test summary info ============================ FAILED xarray/tests/test_dask.py::test_token_identical[obj0-<lambda>1] - AssertionError: assert 'bbd9679bdaf2...d3db65e29a72d' == '6352792990cf...e8004a9055314'

• 6352792990cfe23adb7e8004a9055314

• bbd9679bdaf284c371cd3db65e29a72d FAILED xarray/tests/test_dask.py::test_token_identical[obj0-<lambda>2] - AssertionError: assert 'bbd9679bdaf2...d3db65e29a72d' == '6352792990cf...e8004a9055314'

• 6352792990cfe23adb7e8004a9055314

• bbd9679bdaf284c371cd3db65e29a72d FAILED xarray/tests/test_dask.py::test_token_identical[obj1-<lambda>1] - AssertionError: assert 'c520b8516da8...0e9e0d02b79d0' == '9e2ab1c44990...6ac737226fa02'

• 9e2ab1c44990adb4fb76ac737226fa02

• c520b8516da8b6a98c10e9e0d02b79d0 FAILED xarray/tests/test_dask.py::test_token_identical[obj1-<lambda>2] - AssertionError: assert 'c520b8516da8...0e9e0d02b79d0' == '9e2ab1c44990...6ac737226fa02'

• 9e2ab1c44990adb4fb76ac737226fa02

• c520b8516da8b6a98c10e9e0d02b79d0 = 4 failed, 16293 passed, 628 skipped, 90 xfailed, 71 xpassed, 213 warnings in 472.07s (0:07:52) = Error: Process completed with exit code 1. ```

previously, the following code snippet would pass, verifying the consistency of tokenization in Xarray objects:

```python In [1]: import xarray as xr, numpy as np

In [2]: def make_da(): ...: da = xr.DataArray( ...: np.ones((10, 20)), ...: dims=["x", "y"], ...: coords={"x": np.arange(10), "y": np.arange(100, 120)}, ...: name="a", ...: ).chunk({"x": 4, "y": 5}) ...: da.x.attrs["long_name"] = "x" ...: da.attrs["test"] = "test" ...: da.coords["c2"] = 0.5 ...: da.coords["ndcoord"] = da.x * 2 ...: da.coords["cxy"] = (da.x * da.y).chunk({"x": 4, "y": 5}) ...: ...: return da ...:

In [3]: da = make_da()

In [4]: import dask.base

In [5]: assert dask.base.tokenize(da) == dask.base.tokenize(da.copy(deep=False))

In [6]: assert dask.base.tokenize(da) == dask.base.tokenize(da.copy(deep=True))

In [9]: dask.version Out[9]: '2023.3.0' ```

However, post-update in Dask version '2024.2.1', the same code fails:

```python In [55]: ...: def make_da(): ...: da = xr.DataArray( ...: np.ones((10, 20)), ...: dims=["x", "y"], ...: coords={"x": np.arange(10), "y": np.arange(100, 120)}, ...: name="a", ...: ).chunk({"x": 4, "y": 5}) ...: da.x.attrs["long_name"] = "x" ...: da.attrs["test"] = "test" ...: da.coords["c2"] = 0.5 ...: da.coords["ndcoord"] = da.x * 2 ...: da.coords["cxy"] = (da.x * da.y).chunk({"x": 4, "y": 5}) ...: ...: return da ...:

In [56]: da = make_da() ```

```python In [57]: assert dask.base.tokenize(da) == dask.base.tokenize(da.copy(deep=False))

---

AssertionError Traceback (most recent call last) Cell In[57], line 1 ----> 1 assert dask.base.tokenize(da) == dask.base.tokenize(da.copy(deep=False))

AssertionError:

In [58]: dask.base.tokenize(da) Out[58]: 'bbd9679bdaf284c371cd3db65e29a72d'

In [59]: dask.base.tokenize(da.copy(deep=False)) Out[59]: '6352792990cfe23adb7e8004a9055314'

In [61]: dask.version Out[61]: '2024.2.1' ```

additionally, a deeper dive into dask.base.normalize_token() across the two Dask versions revealed that the latest version includes additional state or metadata in tokenization that was not present in earlier versions.

• old version python In [29]: dask.base.normalize_token((type(da), da._variable, da._coords, da._name)) Out[29]: ('tuple', [xarray.core.dataarray.DataArray, ('tuple', [xarray.core.variable.Variable, ('tuple', ['x', 'y']), 'xarray-<this-array>-14cc91345e4b75c769b9032d473f6f6e', ('list', [('tuple', ['test', 'test'])])]), ('list', [('tuple', ['c2', ('tuple', [xarray.core.variable.Variable, ('tuple', []), (0.5, dtype('float64')), ('list', [])])]), ('tuple', ['cxy', ('tuple', [xarray.core.variable.Variable, ('tuple', ['x', 'y']), 'xarray-<this-array>-8e98950eca22c69d304f0a48bc6c2df9', ('list', [])])]), ('tuple', ['ndcoord', ('tuple', [xarray.core.variable.Variable, ('tuple', ['x']), 'xarray-ndcoord-82411ea5e080aa9b9f554554befc2f39', ('list', [])])]), ('tuple', ['x', ('tuple', [xarray.core.variable.IndexVariable, ('tuple', ['x']), ['x', ('603944b9792513fa0c686bb494a66d96c667f879', dtype('int64'), (10,), (8,))], ('list', [('tuple', ['long_name', 'x'])])])]), ('tuple', ['y', ('tuple', [xarray.core.variable.IndexVariable, ('tuple', ['y']), ['y', ('fc411db876ae0f4734dac8b64152d5c6526a537a', dtype('int64'), (20,), (8,))], ('list', [])])])]), 'a'])

• most recent version

python In [44]: dask.base.normalize_token((type(da), da._variable, da._coords, da._name)) Out[44]: ('tuple', [('7b61e7593a274e48', []), ('tuple', [('215b115b265c420c', []), ('tuple', ['x', 'y']), 'xarray-<this-array>-980383b18aab94069bdb02e9e0956184', ('dict', [('tuple', ['test', 'test'])])]), ('dict', [('tuple', ['c2', ('tuple', [('__seen', 2), ('tuple', []), ('6825817183edbca7', ['48cb5e118059da42']), ('dict', [])])]), ('tuple', ['cxy', ('tuple', [('__seen', 2), ('tuple', ['x', 'y']), 'xarray-<this-array>-6babb4e95665a53f34a3e337129d54b5', ('dict', [])])]), ('tuple', ['ndcoord', ('tuple', [('__seen', 2), ('tuple', ['x']), 'xarray-ndcoord-8636fac37e5e6f4401eab2aef399f402', ('dict', [])])]), ('tuple', ['x', ('tuple', [('abc1995cae8530ae', []), ('tuple', ['x']), ['x', ('99b2df4006e7d28a', ['04673d65c892b5ba'])], ('dict', [('tuple', ['long_name', 'x'])])])]), ('tuple', ['y', ('tuple', [('__seen', 25), ('tuple', ['y']), ['y', ('88974ea603e15c49', ['a6c0f2053e85c87e'])], ('dict', [])])])]), 'a'])

Cc @dcherian / @crusaderky for visibility

What happened?

i'm experiencing compatibility issues when using _arrayfunction_or_api and _sparsearrayfunction_or_api with the sparse arrays with dtype=object. specifically, runtime checks using isinstance with these protocols are failing, despite the sparse array object appearing to meet the necessary criteria (attributes and methods).

What did you expect to happen?

i expected that since COO arrays from the sparse library provide the necessary attributes and methods, they would pass the isinstance checks with the defined protocols.

```python In [56]: from xarray.namedarray._typing import _arrayfunction_or_api, _sparsearrayfunc ...: tion_or_api

In [57]: import xarray as xr, sparse, numpy as np, sparse, pandas as pd ```

• numeric dtypes work

```python In [58]: x = np.random.random((10))

In [59]: x[x < 0.9] = 0

In [60]: s = sparse.COO(x)

In [61]: isinstance(s, _arrayfunction_or_api) Out[61]: True

In [62]: s Out[62]: <COO: shape=(10,), dtype=float64, nnz=0, fill_value=0.0> ```

• string dtypes work

```python In [63]: p = sparse.COO(np.array(['a', 'b']))

In [64]: p Out[64]: <COO: shape=(2,), dtype=<U1, nnz=2, fill_value=>

In [65]: isinstance(s, _arrayfunction_or_api) Out[65]: True ``` - object dtype doesn't work

```python In [66]: q = sparse.COO(np.array(['a', 'b']).astype(object))

In [67]: isinstance(s, _arrayfunction_or_api) Out[67]: True

In [68]: isinstance(q, _arrayfunction_or_api)

TypeError Traceback (most recent call last) File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:606, in _Elemwise._get_func_coords_data(self, mask) 605 try: --> 606 func_data = self.func(func_args, dtype=self.dtype, *self.kwargs) 607 except TypeError:

TypeError: real() got an unexpected keyword argument 'dtype'

During handling of the above exception, another exception occurred:

TypeError Traceback (most recent call last) File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:611, in _Elemwise._get_func_coords_data(self, mask) 610 out = np.empty(func_args[0].shape, dtype=self.dtype) --> 611 func_data = self.func(func_args, out=out, *self.kwargs) 612 except TypeError:

TypeError: real() got an unexpected keyword argument 'out'

During handling of the above exception, another exception occurred:

ValueError Traceback (most recent call last) Cell In[68], line 1 ----> 1 isinstance(q, _arrayfunction_or_api)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/typing.py:1149, in _ProtocolMeta.instancecheck(cls, instance) 1147 return True 1148 if cls._is_protocol: -> 1149 if all(hasattr(instance, attr) and 1150 # All methods can be blocked by setting them to None. 1151 (not callable(getattr(cls, attr, None)) or 1152 getattr(instance, attr) is not None) 1153 for attr in _get_protocol_attrs(cls)): 1154 return True 1155 return super().instancecheck(instance)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/typing.py:1149, in <genexpr>(.0) 1147 return True 1148 if cls._is_protocol: -> 1149 if all(hasattr(instance, attr) and 1150 # All methods can be blocked by setting them to None. 1151 (not callable(getattr(cls, attr, None)) or 1152 getattr(instance, attr) is not None) 1153 for attr in _get_protocol_attrs(cls)): 1154 return True 1155 return super().instancecheck(instance)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_sparse_array.py:900, in SparseArray.real(self) 875 @property 876 def real(self): 877 """The real part of the array. 878 879 Examples (...) 898 numpy.real : NumPy equivalent function. 899 """ --> 900 return self.array_ufunc(np.real, "call", self)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_sparse_array.py:340, in SparseArray.array_ufunc(self, ufunc, method, inputs, kwargs) 337 inputs = tuple(reversed(inputs_transformed)) 339 if method == "call": --> 340 result = elemwise(ufunc, inputs, kwargs) 341 elif method == "reduce": 342 result = SparseArray._reduce(ufunc, *inputs, kwargs)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:49, in elemwise(func, args, kwargs) 12 def elemwise(func, args, kwargs): 13 """ 14 Apply a function to any number of arguments. 15 (...) 46 it is necessary to convert Numpy arrays to :obj:COO objects. 47 """ ---> 49 return _Elemwise(func, *args, kwargs).get_result()

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:480, in _Elemwise.get_result(self) 477 if not any(mask): 478 continue --> 480 r = self._get_func_coords_data(mask) 482 if r is not None: 483 coords_list.append(r[0])

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:613, in _Elemwise._get_func_coords_data(self, mask) 611 func_data = self.func(func_args, out=out, self.kwargs) 612 except TypeError: --> 613 func_data = self.func(func_args, **self.kwargs).astype(self.dtype) 615 unmatched_mask = ~equivalent(func_data, self.fill_value) 617 if not unmatched_mask.any():

ValueError: invalid literal for int() with base 10: 'a'

In [69]: q Out[69]: <COO: shape=(2,), dtype=object, nnz=2, fill_value=0> ```

the failing case appears to be a well know issue

• https://github.com/pydata/sparse/issues/104

Minimal Complete Verifiable Example

```Python In [69]: q Out[69]: <COO: shape=(2,), dtype=object, nnz=2, fill_value=0>

In [70]: n = xr.NamedArray(data=q, dims=['x']) ```

MVCE confirmation

• [ ] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• [ ] Complete example — the example is self-contained, including all data and the text of any traceback.
• [ ] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• [ ] New issue — a search of GitHub Issues suggests this is not a duplicate.
• [ ] Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

```Python In [71]: n.data Out[71]: <COO: shape=(2,), dtype=object, nnz=2, fill_value=0>

In [72]: n Out[72]: --------------------------------------------------------------------------- TypeError Traceback (most recent call last) File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:606, in _Elemwise._get_func_coords_data(self, mask) 605 try: --> 606 func_data = self.func(func_args, dtype=self.dtype, *self.kwargs) 607 except TypeError:

TypeError: real() got an unexpected keyword argument 'dtype'

During handling of the above exception, another exception occurred:

TypeError Traceback (most recent call last) File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:611, in _Elemwise._get_func_coords_data(self, mask) 610 out = np.empty(func_args[0].shape, dtype=self.dtype) --> 611 func_data = self.func(func_args, out=out, *self.kwargs) 612 except TypeError:

TypeError: real() got an unexpected keyword argument 'out'

During handling of the above exception, another exception occurred:

ValueError Traceback (most recent call last) File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/IPython/core/formatters.py:708, in PlainTextFormatter.call(self, obj) 701 stream = StringIO() 702 printer = pretty.RepresentationPrinter(stream, self.verbose, 703 self.max_width, self.newline, 704 max_seq_length=self.max_seq_length, 705 singleton_pprinters=self.singleton_printers, 706 type_pprinters=self.type_printers, 707 deferred_pprinters=self.deferred_printers) --> 708 printer.pretty(obj) 709 printer.flush() 710 return stream.getvalue()

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/IPython/lib/pretty.py:410, in RepresentationPrinter.pretty(self, obj) 407 return meth(obj, self, cycle) 408 if cls is not object \ 409 and callable(cls.dict.get('repr')): --> 410 return _repr_pprint(obj, self, cycle) 412 return _default_pprint(obj, self, cycle) 413 finally:

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/IPython/lib/pretty.py:778, in repr_pprint(obj, p, cycle) 776 """A pprint that just redirects to the normal repr function.""" 777 # Find newlines and replace them with p.break() --> 778 output = repr(obj) 779 lines = output.splitlines() 780 with p.group():

File ~/devel/pydata/xarray/xarray/namedarray/core.py:987, in NamedArray.repr(self) 986 def repr(self) -> str: --> 987 return formatting.array_repr(self)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/reprlib.py:21, in recursive_repr.<locals>.decorating_function.<locals>.wrapper(self) 19 repr_running.add(key) 20 try: ---> 21 result = user_function(self) 22 finally: 23 repr_running.discard(key)

File ~/devel/pydata/xarray/xarray/core/formatting.py:665, in array_repr(arr) 658 name_str = "" 660 if ( 661 isinstance(arr, Variable) 662 or _get_boolean_with_default("display_expand_data", default=True) 663 or isinstance(arr.variable._data, MemoryCachedArray) 664 ): --> 665 data_repr = short_data_repr(arr) 666 else: 667 data_repr = inline_variable_array_repr(arr.variable, OPTIONS["display_width"])

File ~/devel/pydata/xarray/xarray/core/formatting.py:633, in short_data_repr(array) 631 if isinstance(array, np.ndarray): 632 return short_array_repr(array) --> 633 elif isinstance(internal_data, _arrayfunction_or_api): 634 return limit_lines(repr(array.data), limit=40) 635 elif getattr(array, "_in_memory", None):

File ~/mambaforge/envs/xarray-tests/lib/python3.9/typing.py:1149, in _ProtocolMeta.instancecheck(cls, instance) 1147 return True 1148 if cls._is_protocol: -> 1149 if all(hasattr(instance, attr) and 1150 # All methods can be blocked by setting them to None. 1151 (not callable(getattr(cls, attr, None)) or 1152 getattr(instance, attr) is not None) 1153 for attr in _get_protocol_attrs(cls)): 1154 return True 1155 return super().instancecheck(instance)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/typing.py:1149, in <genexpr>(.0) 1147 return True 1148 if cls._is_protocol: -> 1149 if all(hasattr(instance, attr) and 1150 # All methods can be blocked by setting them to None. 1151 (not callable(getattr(cls, attr, None)) or 1152 getattr(instance, attr) is not None) 1153 for attr in _get_protocol_attrs(cls)): 1154 return True 1155 return super().instancecheck(instance)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_sparse_array.py:900, in SparseArray.real(self) 875 @property 876 def real(self): 877 """The real part of the array. 878 879 Examples (...) 898 numpy.real : NumPy equivalent function. 899 """ --> 900 return self.array_ufunc(np.real, "call", self)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_sparse_array.py:340, in SparseArray.array_ufunc(self, ufunc, method, inputs, kwargs) 337 inputs = tuple(reversed(inputs_transformed)) 339 if method == "call": --> 340 result = elemwise(ufunc, inputs, kwargs) 341 elif method == "reduce": 342 result = SparseArray._reduce(ufunc, *inputs, kwargs)

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:49, in elemwise(func, args, kwargs) 12 def elemwise(func, args, kwargs): 13 """ 14 Apply a function to any number of arguments. 15 (...) 46 it is necessary to convert Numpy arrays to :obj:COO objects. 47 """ ---> 49 return _Elemwise(func, *args, kwargs).get_result()

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:480, in _Elemwise.get_result(self) 477 if not any(mask): 478 continue --> 480 r = self._get_func_coords_data(mask) 482 if r is not None: 483 coords_list.append(r[0])

File ~/mambaforge/envs/xarray-tests/lib/python3.9/site-packages/sparse/_umath.py:613, in _Elemwise._get_func_coords_data(self, mask) 611 func_data = self.func(func_args, out=out, self.kwargs) 612 except TypeError: --> 613 func_data = self.func(func_args, **self.kwargs).astype(self.dtype) 615 unmatched_mask = ~equivalent(func_data, self.fill_value) 617 if not unmatched_mask.any():

ValueError: invalid literal for int() with base 10: 'a' ```

Anything else we need to know?

i was trying to replace instances of is_duck_array with the protocol runtime checks (as part of https://github.com/pydata/xarray/pull/8319), and i've come to a realization that these runtime checks are rigid to accommodate the diverse behaviors of different array types, and is_duck_array() the function-based approach might be more manageable.

@Illviljan, are there any changes that could be made to both protocols without making them too complex?

Environment

```python INSTALLED VERSIONS ------------------ commit: 541049f45edeb518a767cb3b23fa53f6045aa508 python: 3.9.18 | packaged by conda-forge | (main, Dec 23 2023, 16:35:41) [Clang 16.0.6 ] python-bits: 64 OS: Darwin OS-release: 23.2.0 machine: arm64 processor: arm byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: ('en_US', 'UTF-8') libhdf5: 1.14.3 libnetcdf: 4.9.2 xarray: 2024.1.2.dev50+g78dec61f pandas: 2.2.0 numpy: 1.26.3 scipy: 1.12.0 netCDF4: 1.6.5 pydap: installed h5netcdf: 1.3.0 h5py: 3.10.0 Nio: None zarr: 2.16.1 cftime: 1.6.3 nc_time_axis: 1.4.1 iris: 3.7.0 bottleneck: 1.3.7 dask: 2024.1.1 distributed: 2024.1.1 matplotlib: 3.8.2 cartopy: 0.22.0 seaborn: 0.13.2 numbagg: 0.7.1 fsspec: 2023.12.2 cupy: None pint: 0.23 sparse: 0.15.1 flox: 0.9.0 numpy_groupies: 0.9.22 setuptools: 67.7.2 pip: 23.3.2 conda: None pytest: 8.0.0 mypy: 1.8.0 IPython: 8.14.0 sphinx: None ```

What is your issue?

A recent release of pytest (v8.0.0) appears to have broken our CI.

bash pytest 8.0.0 pyhd8ed1ab_0 conda-forge pytest-cov 4.1.0 pyhd8ed1ab_0 conda-forge pytest-env 1.1.3 pyhd8ed1ab_0 conda-forge pytest-github-actions-annotate-failures 0.2.0 pypi_0 pypi pytest-timeout 2.2.0 pyhd8ed1ab_0 conda-forge pytest-xdist 3.5.0 pyhd8ed1ab_0 conda-forge

Strangely, the issue doesn't seem to occur when using previous versions (e.g. v7.4.4). our last successful CI run used pytest v7.4.4

bash pytest 7.4.4 pyhd8ed1ab_0 conda-forge pytest-cov 4.1.0 pyhd8ed1ab_0 conda-forge pytest-env 1.1.3 pyhd8ed1ab_0 conda-forge pytest-github-actions-annotate-failures 0.2.0 pypi_0 pypi pytest-timeout 2.2.0 pyhd8ed1ab_0 conda-forge pytest-xdist 3.5.0 pyhd8ed1ab_0 conda-forge

i recreated the environment and successfully ran tests locally. the CI failures appear to be connected to the latest release of pytest. i haven't had a chance to do an in-depth exploration of the changes from pytest which could be influencing this disruption. so, i wanted to open an issue to track what is going on. in the meantime, i'm going to pin pytest to an earlier version.

any insights, especially from those familiar with changes in the pytest v8.0.0 update, are warmly welcomed.

Is your feature request related to a problem? Please describe.

I'm working on some caching/data-provenance functionality for xarray objects, and I realized that there's no standard/efficient way of computing hashes for xarray objects.

Describe the solution you'd like

It would be useful to have a configurable, reliable/standard .hexdigest() method on xarray objects. For example, zarr provides a digest method that returns you a digest/hash of the data.

```python In [16]: import zarr

In [17]: z = zarr.zeros(shape=(10000, 10000), chunks=(1000, 1000))

In [18]: z.hexdigest() # uses sha1 by default for speed Out[18]: '7162d416d26a68063b66ed1f30e0a866e4abed60'

In [20]: z.hexdigest(hashname='sha256') Out[20]: '46fc6e52fc1384e37cead747075f55201667dd539e4e72d0f372eb45abdcb2aa' ```

I'm thinking that an xarray's built-in hashing mechanism would provide a more reliable way to treat metadata such as global attributes, encoding, etc... during the hash computation...

Describe alternatives you've considered

So far, I am using joblib's default hasher: joblib.hash() function. However, I am in favor of having a configurable/built-in hasher that is aware of xarray's data model and quirks :)

```python In [1]: import joblib

In [2]: import xarray as xr

In [3]: ds = xr.tutorial.open_dataset('rasm')

In [5]: joblib.hash(ds, hash_name='sha1') Out[5]: '3e5e3f56daf81e9e04a94a3dff9fdca9638c36cf'

In [8]: ds.attrs = {}

In [9]: joblib.hash(ds, hash_name='sha1') Out[9]: 'daab25fe735657e76514040608fadc67067d90a0' ```

Additional context Add any other context about the feature request here.

None is not really practical in current xarray so not allowing it as a dimension is probably the easiest path, but type hinting will not be correct.

I want dims to have a type hint that is consistent, easy to read and understand. In a dream world it would look something like this: python InputDim = Hashable # Single dimension InputDims = Iterable[InputDim , ...] # multiple dimensions InputDimOrDims = Union[InputDim, InputDims] # Single or multiple dimensions

Then we can easily go through our xarray methods and easily replace dim and dims arguments.

Hashable could be fine in NamedArray, we haven't introduced None as a typical default value there yet.

But it wouldn't be easy in xarray because we use None as default value a lot, which will (I suspect) lead to a bunch of refactoring and deprecations. I haven't tried it maybe it's doable?

Another idea is to try and make a HashableExcludingNone: python HashableExcludingNone = Union[int, str, tuple, ...] # How many more Hashables are there? InputDim = HashableExcludingNone # Single dimension InputDims = Iterable[InputDim , ...] # multiple dimensions InputDimOrDims = Union[InputDim, InputDims] # Single or multiple dimensions I suspect this is harder than it seems.

Another idea is drop the idea of Hashable and just allow a few common ones that are used: python InputDim = str # Single dimension InputDims = tuple[InputDim , ...] # multiple dimensions InputDimOrDims = Union[InputDim, InputDims] # Single or multiple dimensions Very clear! I think a few users (and maintainers) will be sad because of the lack of flexibility though.

No easy paths, and trying to be backwards compatible is very demotivating.

Originally posted by @Illviljan in https://github.com/pydata/xarray/pull/8075#discussion_r1330437962

Currently, when xarray.coding.times.encode_cf_datetime() is called, it always casts the input to a NumPy array. This is not what I would expect when the input is a dask array. I am wondering if we could make this operation lazy when the input is a dask array?

https://github.com/pydata/xarray/blob/01462d65c7213e5e1cddf36492c6a34a7e53ce55/xarray/coding/times.py#L352-L354

```python In [46]: import numpy as np

In [47]: import xarray as xr

In [48]: import pandas as pd

In [49]: times = pd.date_range("2000-01-01", "2001-01-01", periods=11)

In [50]: time_bounds = np.vstack((times[:-1], times[1:])).T

In [51]: arr = xr.DataArray(time_bounds).chunk()

In [52]: arr
Out[52]: <xarray.DataArray (dim_0: 10, dim_1: 2)> dask.array<xarray-\<this-array>, shape=(10, 2), dtype=datetime64[ns], chunksize=(10, 2), chunktype=numpy.ndarray> Dimensions without coordinates: dim_0, dim_1

In [53]: xr.coding.times.encode_cf_datetime(arr)
Out[53]: (array([[ 0, 52704], [ 52704, 105408], [105408, 158112], [158112, 210816], [210816, 263520], [263520, 316224], [316224, 368928], [368928, 421632], [421632, 474336], [474336, 527040]]), 'minutes since 2000-01-01 00:00:00', 'proleptic_gregorian')

```

Cc @jhamman

What happened:

While using xr.save_mfdataset() function with compute=False I noticed that the function returns a dask.delayed object, but it doesn't actually defer the computation i.e. it actually writes datasets right away.

What you expected to happen:

I expect the datasets to be written when I explicitly call .compute() on the returned delayed object.

Minimal Complete Verifiable Example:

```python In [2]: import xarray as xr

In [3]: ds = xr.tutorial.open_dataset('rasm', chunks={})

In [4]: ds Out[4]: <xarray.Dataset> Dimensions: (time: 36, x: 275, y: 205) Coordinates: * time (time) object 1980-09-16 12:00:00 ... 1983-08-17 00:00:00 xc (y, x) float64 dask.array<chunksize=(205, 275), meta=np.ndarray> yc (y, x) float64 dask.array<chunksize=(205, 275), meta=np.ndarray> Dimensions without coordinates: x, y Data variables: Tair (time, y, x) float64 dask.array<chunksize=(36, 205, 275), meta=np.ndarray> Attributes: title: /workspace/jhamman/processed/R1002RBRxaaa01a/l... institution: U.W. source: RACM R1002RBRxaaa01a output_frequency: daily output_mode: averaged convention: CF-1.4 references: Based on the initial model of Liang et al., 19... comment: Output from the Variable Infiltration Capacity... nco_openmp_thread_number: 1 NCO: "4.6.0" history: Tue Dec 27 14:15:22 2016: ncatted -a dimension...

In [5]: path = "test.nc"

In [7]: ls -ltrh test.nc ls: cannot access test.nc: No such file or directory

In [8]: tasks = xr.save_mfdataset(datasets=[ds], paths=[path], compute=False)

In [9]: tasks Out[9]: Delayed('list-aa0b52e0-e909-4e65-849f-74526d137542')

In [10]: ls -ltrh test.nc -rw-r--r-- 1 abanihi ncar 14K Jul 8 10:29 test.nc ```

Anything else we need to know?:

Environment:

Output of <tt>xr.show_versions()</tt>

```python INSTALLED VERSIONS ------------------ commit: None python: 3.7.6 | packaged by conda-forge | (default, Jun 1 2020, 18:57:50) [GCC 7.5.0] python-bits: 64 OS: Linux OS-release: 3.10.0-693.21.1.el7.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: en_US.UTF-8 LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.5 libnetcdf: 4.7.4 xarray: 0.15.1 pandas: 0.25.3 numpy: 1.18.5 scipy: 1.5.0 netCDF4: 1.5.3 pydap: None h5netcdf: None h5py: 2.10.0 Nio: None zarr: None cftime: 1.2.0 nc_time_axis: 1.2.0 PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.20.0 distributed: 2.20.0 matplotlib: 3.2.1 cartopy: None seaborn: None numbagg: None setuptools: 49.1.0.post20200704 pip: 20.1.1 conda: None pytest: None IPython: 7.16.1 sphinx: None ```

xr.Dataset reduce methods such as mean drop non-numeric data variables prior to the reduction. However, as far as I can tell this info isn't mentioned anywhere in the documentation/docstrings. I think this would be useful information to include here for example:

```python In [47]: import xarray as xr

In [48]: import numpy as np, pandas as pd

In [50]: ds['foo'] = xr.DataArray(np.arange(6).reshape(2, 3), dims=['x', 'y'])

In [53]: ds['bar'] = xr.DataArray(pd.date_range(start='2000', periods=6).values.reshape(2, 3), dims=['x', 'y'])

In [54]: ds Out[54]: <xarray.Dataset> Dimensions: (x: 2, y: 3) Dimensions without coordinates: x, y Data variables: foo (x, y) int64 0 1 2 3 4 5 bar (x, y) datetime64[ns] 2000-01-01 2000-01-02 ... 2000-01-06 ```

```python In [55]: ds.mean('x') Out[55]: <xarray.Dataset> Dimensions: (y: 3) Dimensions without coordinates: y Data variables: foo (y) float64 1.5 2.5 3.5

In [56]: ds.bar.mean('x') Out[56]: <xarray.DataArray 'bar' (y: 3)> array(['2000-01-02T12:00:00.000000000', '2000-01-03T12:00:00.000000000', '2000-01-04T12:00:00.000000000'], dtype='datetime64[ns]') Dimensions without coordinates: y ```

Currently, xarray has a room on Gitter: https://gitter.im/pydata/xarray. This room works fine for discussions outside of the codebase. However, Gitter has a few disadvantages:

• The contents are not indexed by search engines
• Searching through existing discussions is almost impossible
• Linking to prior conversations in the room is also complicated

A few months ago, GitHub announced GitHub discussions which is meant to serve as a forum for discussions outside of the codebase. I am of the opinion that GitHub discussions is a better alternative to Gitter. I am wondering if xarray folks would be interested in enabling GitHub discussion on this repo, and migrating general discussions from Gitter to GitHub discussions?

GitHub Discussions is still in beta, but projects can request early access here

Here is a list of a few projects with beta access:

• https://github.com/vercel/vercel/discussions
• https://github.com/KaTeX/KaTeX/discussions
• https://github.com/vercel/next.js/discussions

Is your feature request related to a problem? Please describe.

Currently, when a user wants to write multiple netCDF files in parallel with xarray and dask, they can take full advantage of xr.save_mfdataset() function. This function in its current state works fine, but the existing API requires that - the user generates file paths themselves - the user maps each chunk or dataset to a corresponding output file

A few months ago, I wrote a blog post showing how to save an xarray dataset backed by dask into multiple netCDF files, and since then I've been meaning to request a new feature to make this process convenient for users.

Describe the solution you'd like

Would it be useful to actually refactor the existing xr.save_mfdataset() to automatically save an xarray object backed by dask arrays to multiple files without needing to create paths ourselves? Today, this can be achieved via xr.map_blocks. In other words, is it possible to have something analogous to to_zarr(....) but for netCDF:

```python ds.save_mfdataset(prefix="directory/my-dataset")

or

xr.save_mfdataset(ds, prefix="directoy/my-dataset")

```

---->

```bash

directory/my-dataset-chunk-1.nc directory/my-dataset-chunk-2.nc directory/my-dataset-chunk-3.nc .... ```

What happened:

While computing averaged time using time_bounds via times = bounds.mean('d2'), I get weird results (see example below). It's my understanding that this is a bug, but I don't know yet where it's coming from. I should note that in addition to getting wrong time values, the resulting time values are not monotonically increasing even though my time bounds are.

What you expected to happen:

Correct averaged time values

Minimal Complete Verifiable Example:

```python In [1]: import xarray as xr

In [2]: import numpy as np

In [3]: dates = xr.cftime_range(start='0400-01', end='2101-01', freq='120Y', calendar='noleap')

In [4]: bounds = xr.DataArray(np.vstack([dates[:-1], dates[1:]]).T, dims=['time', 'd2'])

In [5]: bounds
Out[5]: <xarray.DataArray (time: 14, d2: 2)> array([[cftime.DatetimeNoLeap(400, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(520, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(520, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(640, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(640, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(760, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(760, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(880, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(880, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1000, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1000, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1120, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1120, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1240, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1240, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1360, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1360, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1480, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1480, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1600, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1600, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1720, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1720, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1840, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1840, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(1960, 12, 31, 0, 0, 0, 0)], [cftime.DatetimeNoLeap(1960, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(2080, 12, 31, 0, 0, 0, 0)]], dtype=object) Dimensions without coordinates: time, d2

In [6]: bounds.mean('d2')
Out[6]: <xarray.DataArray (time: 14)> array([cftime.DatetimeNoLeap(460, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(580, 12, 31, 0, 0, 0, 0), cftime.DatetimeNoLeap(116, 1, 21, 0, 25, 26, 290448), cftime.DatetimeNoLeap(236, 1, 21, 0, 25, 26, 290448), cftime.DatetimeNoLeap(356, 1, 21, 0, 25, 26, 290448), cftime.DatetimeNoLeap(476, 1, 21, 0, 25, 26, 290448), cftime.DatetimeNoLeap(596, 1, 21, 0, 25, 26, 290448), cftime.DatetimeNoLeap(131, 2, 11, 0, 50, 52, 580897), cftime.DatetimeNoLeap(251, 2, 11, 0, 50, 52, 580897), cftime.DatetimeNoLeap(371, 2, 11, 0, 50, 52, 580897), cftime.DatetimeNoLeap(491, 2, 11, 0, 50, 52, 580897), cftime.DatetimeNoLeap(611, 2, 11, 0, 50, 52, 580897), cftime.DatetimeNoLeap(146, 3, 4, 1, 16, 18, 871345), cftime.DatetimeNoLeap(266, 3, 4, 1, 16, 18, 871345)], dtype=object) Dimensions without coordinates: time

```

Anything else we need to know?:

Environment:

Output of <tt>xr.show_versions()</tt>

```python INSTALLED VERSIONS ------------------ commit: None python: 3.7.8 | packaged by conda-forge | (default, Jul 23 2020, 03:54:19) [GCC 7.5.0] python-bits: 64 OS: Linux OS-release: 3.10.0-1127.13.1.el7.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: en_US.UTF-8 LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.6 libnetcdf: 4.7.4 xarray: 0.16.0 pandas: 1.1.0 numpy: 1.19.1 scipy: 1.5.2 netCDF4: 1.5.4 pydap: None h5netcdf: None h5py: 2.10.0 Nio: None zarr: 2.4.0 cftime: 1.2.1 nc_time_axis: 1.2.0 PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.22.0 distributed: 2.22.0 matplotlib: 3.3.0 cartopy: 0.18.0 seaborn: 0.10.1 numbagg: None pint: None setuptools: 49.2.1.post20200802 pip: 20.2.1 conda: None pytest: None IPython: 7.17.0 sphinx: None ```

I just updated to the latest cftime release, and all of a sudden sel() appears to be broken:

```python In [1]: import xarray as xr

In [2]: import cftime

In [3]: ds = xr.tutorial.load_dataset('rasm')

In [4]: ds
Out[4]: <xarray.Dataset> Dimensions: (time: 36, x: 275, y: 205) Coordinates: * time (time) object 1980-09-16 12:00:00 ... 1983-08-17 00:00:00 xc (y, x) float64 189.2 189.4 189.6 189.7 ... 17.65 17.4 17.15 16.91 yc (y, x) float64 16.53 16.78 17.02 17.27 ... 28.26 28.01 27.76 27.51 Dimensions without coordinates: x, y Data variables: Tair (time, y, x) float64 nan nan nan nan nan ... 29.8 28.66 28.19 28.21 Attributes: title: /workspace/jhamman/processed/R1002RBRxaaa01a/l... institution: U.W. source: RACM R1002RBRxaaa01a output_frequency: daily output_mode: averaged convention: CF-1.4 references: Based on the initial model of Liang et al., 19... comment: Output from the Variable Infiltration Capacity... nco_openmp_thread_number: 1 NCO: "4.6.0" history: Tue Dec 27 14:15:22 2016: ncatted -a dimension...

In [5]: ds.sel(time=slice("1980", "1982"))

ValueError Traceback (most recent call last) <ipython-input-5-2c26e36a673a> in <module> ----> 1 ds.sel(time=slice("1980", "1982"))

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/xarray/core/dataset.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs) 1998 indexers = either_dict_or_kwargs(indexers, indexers_kwargs, "sel") 1999 pos_indexers, new_indexes = remap_label_indexers( -> 2000 self, indexers=indexers, method=method, tolerance=tolerance 2001 ) 2002 result = self.isel(indexers=pos_indexers, drop=drop)

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/xarray/core/coordinates.py in remap_label_indexers(obj, indexers, method, tolerance, **indexers_kwargs) 390 391 pos_indexers, new_indexes = indexing.remap_label_indexers( --> 392 obj, v_indexers, method=method, tolerance=tolerance 393 ) 394 # attach indexer's coordinate to pos_indexers

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/xarray/core/indexing.py in remap_label_indexers(data_obj, indexers, method, tolerance) 259 coords_dtype = data_obj.coords[dim].dtype 260 label = maybe_cast_to_coords_dtype(label, coords_dtype) --> 261 idxr, new_idx = convert_label_indexer(index, label, dim, method, tolerance) 262 pos_indexers[dim] = idxr 263 if new_idx is not None:

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/xarray/core/indexing.py in convert_label_indexer(index, label, index_name, method, tolerance) 123 _sanitize_slice_element(label.start), 124 _sanitize_slice_element(label.stop), --> 125 _sanitize_slice_element(label.step), 126 ) 127 if not isinstance(indexer, slice):

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/pandas/core/indexes/base.py in slice_indexer(self, start, end, step, kind) 5032 slice(1, 3) 5033 """ -> 5034 start_slice, end_slice = self.slice_locs(start, end, step=step, kind=kind) 5035 5036 # return a slice

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/pandas/core/indexes/base.py in slice_locs(self, start, end, step, kind) 5246 start_slice = None 5247 if start is not None: -> 5248 start_slice = self.get_slice_bound(start, "left", kind) 5249 if start_slice is None: 5250 start_slice = 0

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/pandas/core/indexes/base.py in get_slice_bound(self, label, side, kind) 5158 # For datetime indices label may be a string that has to be converted 5159 # to datetime boundary according to its resolution. -> 5160 label = self._maybe_cast_slice_bound(label, side, kind) 5161 5162 # we need to look up the label

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/xarray/coding/cftimeindex.py in _maybe_cast_slice_bound(self, label, side, kind) 336 pandas.tseries.index.DatetimeIndex._maybe_cast_slice_bound""" 337 if isinstance(label, str): --> 338 parsed, resolution = _parse_iso8601_with_reso(self.date_type, label) 339 start, end = _parsed_string_to_bounds(self.date_type, resolution, parsed) 340 if self.is_monotonic_decreasing and len(self) > 1:

~/opt/miniconda3/envs/intake-esm-dev/lib/python3.7/site-packages/xarray/coding/cftimeindex.py in _parse_iso8601_with_reso(date_type, timestr) 114 # 1.0.3.4. 115 replace["dayofwk"] = -1 --> 116 return default.replace(**replace), resolution 117 118

cftime/_cftime.pyx in cftime._cftime.datetime.replace()

ValueError: Replacing the dayofyr or dayofwk of a datetime is not supported.

```

Output of xr.show_versions()

# Paste the output here xr.show_versions() here ```python In [6]: xr.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 3.7.3 | packaged by conda-forge | (default, Jul 1 2019, 14:38:56) [Clang 4.0.1 (tags/RELEASE_401/final)] python-bits: 64 OS: Darwin OS-release: 18.7.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.5 libnetcdf: 4.7.1 xarray: 0.14.0 pandas: 0.25.2 numpy: 1.17.2 scipy: None netCDF4: 1.5.1.2 pydap: None h5netcdf: None h5py: None Nio: None zarr: 2.3.2 cftime: 1.0.4 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.2.0 distributed: 2.5.1 matplotlib: None cartopy: None seaborn: None numbagg: None setuptools: 41.4.0 pip: 19.2.1 conda: None pytest: 5.0.1 IPython: 7.8.0 sphinx: 2.1.2 ```

Expected Output

I can confirm that everything works just fine with an older version of cftime:

```python In [4]: ds.sel(time=slice("1980", "1982"))
Out[4]: <xarray.Dataset> Dimensions: (time: 28, x: 275, y: 205) Coordinates: * time (time) object 1980-09-16 12:00:00 ... 1982-12-17 00:00:00 xc (y, x) float64 ... yc (y, x) float64 ... Dimensions without coordinates: x, y Data variables: Tair (time, y, x) float64 ... Attributes: title: /workspace/jhamman/processed/R1002RBRxaaa01a/l... institution: U.W. source: RACM R1002RBRxaaa01a output_frequency: daily output_mode: averaged convention: CF-1.4 references: Based on the initial model of Liang et al., 19... comment: Output from the Variable Infiltration Capacity... nco_openmp_thread_number: 1 NCO: "4.6.0" history: Tue Dec 27 14:15:22 2016: ncatted -a dimension... In [5]: import cftime

In [6]: cftime.version
Out[6]: '1.0.3.4'

In [7]: xr.version
Out[7]: '0.14.0' ```