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
1160062673,I_kwDOAMm_X85FJSbR,6333,Expressing dimension's preferred chunks as tuple of integers causes TypeError,38358698,closed,0,,,0,2022-03-04T21:23:21Z,2022-04-08T17:18:50Z,2022-04-08T17:18:50Z,CONTRIBUTOR,,,,"### What happened?

When opening a dataset containing a variable that has preferred chunks expressed along some dimension as a tuple of integers, *xarray* raises a `TypeError`.

### What did you expect to happen?

I expected to open the dataset with its preferred chunks, as described in the documentation on preferred chunks within ""How to add a new backend"".

### Minimal Complete Verifiable Example

```Python
import xarray as xr

class PassThroughBackendEntrypoint(xr.backends.BackendEntrypoint):
    def open_dataset(self, dataset, *, drop_variables=None):
        return dataset

initial = xr.Dataset(
    {
        ""data"": xr.Variable(
            (""dim"",), [0, 0], encoding={""preferred_chunks"": {""dim"": (1, 1)}}
        )
    }
)
final = xr.open_dataset(initial, engine=PassThroughBackendEntrypoint, chunks={})
```


### Relevant log output

```Python
[Paths simplified.]

Traceback (most recent call last):
  File ""<stdin>"", line 1, in <module>
  File ""...\xarray\backends\api.py"", line 501, in open_dataset
    ds = _dataset_from_backend_dataset(
  File ""...\xarray\backends\api.py"", line 317, in _dataset_from_backend_dataset
    ds = _chunk_ds(
  File ""...\xarray\backends\api.py"", line 287, in _chunk_ds
    var_chunks = _get_chunk(var, chunks)
  File ""...\xarray\core\dataset.py"", line 409, in _get_chunk

    _check_chunks_compatibility(var, output_chunks, preferred_chunks)
  File ""...\xarray\core\dataset.py"", line 371, in _check_chunks_compatibility
    if any(s % preferred_chunks_dim for s in chunks_dim):
  File ""...\xarray\core\dataset.py"", line 371, in <genexpr>
    if any(s % preferred_chunks_dim for s in chunks_dim):
TypeError: unsupported operand type(s) for %: 'int' and 'tuple'
```


### Anything else we need to know?

The behavior exhibited above touches on the following related issues:

*   The `_check_chunks_compatibility` function assumes that a dimension expresses its preferred chunks only as an integer, not a sequence of integers.  In contrast, *Dask* will handle either within the `previous_chunks` argument to its `normalize_chunks` function.

*   The examples in the documentation of `""preferred_chunks""` mappings, namely `{“dim1”: 1000, “dim2”: 2000}` and `{“dim1”: [1000, 100], “dim2”: [2000, 2000, 2000]]}`, have syntax errors: The quotation marks are curly instead of straight, and the second example has an extra closing bracket.

*   After correcting the syntax errors, the lists in the second example lead to `TypeError: unhashable type: 'list'`.  *Dask* raises the exception when it tries to test a mutable list for set membership, as in the following (with simplified paths):

    ```python
    >>> dask.array.core.normalize_chunks([[1000, 100], [2000, 2000, 2000]], (1100, 6000))
    Traceback (most recent call last):
      File ""<stdin>"", line 1, in <module>
      File ""...\dask\array\core.py"", line 2900, in normalize_chunks
        chunks = tuple(c if c not in {None, -1} else s for c, s in zip(chunks, shape))
      File ""...\dask\array\core.py"", line 2900, in <genexpr>
        chunks = tuple(c if c not in {None, -1} else s for c, s in zip(chunks, shape))
    TypeError: unhashable type: 'list'
    ```

    If one omits the second argument (the shape) to that call, it succeeds.  This may be a bug in *Dask*.

*   The tests in *xarray* don't exercise behaviors related to preferred chunks.

[Edited for grammar.]

### Environment

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.8.12 | packaged by conda-forge | (default, Oct 12 2021, 21:22:46) [MSC v.1916 64 bit (AMD64)]
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 94 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('English_United States', '1252')
libhdf5: 1.12.1
libnetcdf: 4.8.1

xarray: 0.20.3.dev52+gd3b6aa6d
pandas: 1.4.1
numpy: 1.21.5
scipy: 1.8.0
netCDF4: 1.5.8
pydap: installed
h5netcdf: 0.13.1
h5py: 3.6.0
Nio: None
zarr: 2.11.0
cftime: 1.5.2
nc_time_axis: 1.4.0
PseudoNetCDF: installed
rasterio: 1.2.10
cfgrib: None
iris: 3.2.0.post0
bottleneck: 1.3.2
dask: 2022.02.0
distributed: 2022.02.0
matplotlib: 3.5.1
cartopy: 0.20.2
seaborn: 0.11.2
numbagg: 0.2.1
fsspec: 2022.01.0
cupy: None
pint: 0.18
sparse: 0.13.0
setuptools: 59.8.0
pip: 22.0.3
conda: None
pytest: 7.0.1
IPython: None
sphinx: None
```","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6333/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue