issue_comments: 851618811

Will it not cripple performance due to the non-lazy evaluation of the list ?

I also started the test for the concat function, I discovered that if the first element determine between _dataarray_concat and _dataset_concat. I am not sure if I need to do several commits (type checking dataset, type checking data array) and several test.

Here is the draft for the tests: ``` def test_concat_check_input_type(): ds = Dataset({"foo": 1}, {"bar": 2}) da = Dataset({"foo": 3}, {"bar": 4}).to_array(dim='foo')

# concatenate a list of non-homogeneous types must raise TypeError
with pytest.raises(TypeError, match="Some elements in the input list datasets are not 'DataSet'"):
    concat([ds, da], dim="foo")

# concatenate a list of non-homogeneous types must raise TypeError
with pytest.raises(TypeError, match="Some elements in the input list datasets are not 'DataArray'"):
    concat([da, ds], dim="foo")

```

Code I plan to add also for the typing check in _dataarray_concat: from .dataarray import DataArray arrays = list(arrays) if not all(isinstance(array, DataArray) for array in list(arrays)): raise TypeError("Some elements in the input list datasets are not 'DataArray'") (I need to add from .dataarray import DataArray to be able to use the type)