Hi @airton-neto - here is a much shorter example that reproduces the same error

```python url = 'https://rda.ucar.edu/thredds/dodsC/files/g/ds084.1/2022/20220201/gfs.0p25.2022020100.f000.grib2'

dataset = xr.open_dataset(url, cache=True, engine="netcdf4") python from dagster._utils import frozenlist

variables = list(['u-component_of_wind_height_above_ground']) # <--- This way it runs

variables = frozenlist(['u-component_of_wind_height_above_ground'])

dataset[variables] ```

```python

KeyError Traceback (most recent call last) File ~/miniconda3/envs/py39/lib/python3.9/site-packages/xarray/core/dataset.py:1317, in Dataset._construct_dataarray(self, name) 1316 try: -> 1317 variable = self._variables[name] 1318 except KeyError:

KeyError: ['u-component_of_wind_height_above_ground']

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last) Input In [43], in <cell line: 1>() ----> 1 dataset[variables]

File ~/miniconda3/envs/py39/lib/python3.9/site-packages/xarray/core/dataset.py:1410, in Dataset.getitem(self, key) 1408 return self.isel(**key) 1409 if utils.hashable(key): -> 1410 return self._construct_dataarray(key) 1411 if utils.iterable_of_hashable(key): 1412 return self._copy_listed(key)

File ~/miniconda3/envs/py39/lib/python3.9/site-packages/xarray/core/dataset.py:1319, in Dataset.construct_dataarray(self, name) 1317 variable = self._variables[name] 1318 except KeyError: -> 1319 , name, variable = _get_virtual_variable(self._variables, name, self.dims) 1321 needed_dims = set(variable.dims) 1323 coords: dict[Hashable, Variable] = {}

File ~/miniconda3/envs/py39/lib/python3.9/site-packages/xarray/core/dataset.py:171, in _get_virtual_variable(variables, key, dim_sizes) 168 return key, key, variable 170 if not isinstance(key, str): --> 171 raise KeyError(key) 173 split_key = key.split(".", 1) 174 if len(split_key) != 2:

KeyError: ['u-component_of_wind_height_above_ground'] ```

I'm not immediately sure why the elements of the list are not properly extracted, but the frozenlist class is a dagster private internal, and the problem is specific to how that object interacts with the current xarray code. As a downstream user of xarray, can dagster not just change it's code to pass the type xarray expects (i.e. a normal list)?

Having said that if you want to submit a PR which fixes this bug (and doesn't require special-casing dagster somehow) then that would be welcome too!