_indexes of DataArray are not deep copied

[toddrjen]

In DataArray.copy, the _indexes attributes is not deep copied. After pull request #3840, this causes deleting a coordinate of a copy will also delete that coordinate from the original, even for deep copies.

MCVE Code Sample

a0 = xr.DataArray(
    np.array([[1, 2, 3], [4, 5, 6]]),
    dims=["y", "x"],
    coords={"x": ["a", "b", "c"], "y": [-1, 1]},
)

a1 = a0.copy()
del a1.coords["y"]

xr.tests.assert_identical(a0, a0)

The result is:

xarray/testing.py:272: in _assert_internal_invariants
    _assert_dataarray_invariants(xarray_obj)
xarray/testing.py:222: in _assert_dataarray_invariants
    _assert_indexes_invariants_checks(da._indexes, da._coords, da.dims)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

indexes = {'x': Index(['a', 'b', 'c'], dtype='object', name='x')}, possible_coord_variables = {'x': <xarray.IndexVariable 'x' (x: 3)>
array(['a', 'b', 'c'], dtype='<U1'), 'y': <xarray.IndexVariable 'y' (y: 2)>
array([-1,  1])}
dims = ('y', 'x')

    def _assert_indexes_invariants_checks(indexes, possible_coord_variables, dims):
        assert isinstance(indexes, dict), indexes
        assert all(isinstance(v, pd.Index) for v in indexes.values()), {
            k: type(v) for k, v in indexes.items()
        }
    
        index_vars = {
            k for k, v in possible_coord_variables.items() if isinstance(v, IndexVariable)
        }
        assert indexes.keys() <= index_vars, (set(indexes), index_vars)
    
        # Note: when we support non-default indexes, these checks should be opt-in
        # only!
        defaults = default_indexes(possible_coord_variables, dims)
>       assert indexes.keys() == defaults.keys(), (set(indexes), set(defaults))
E       AssertionError: ({'x'}, {'y', 'x'})

xarray/testing.py:185: AssertionError

Expected Output

The test should pass.

Problem Description

Doing a deep copy should make a copy of everything. Changing a deep copy should not alter the original in any way.

[max-sixty]

Great spot @toddrjen .

@dcherian any ideas? I may have some spare time tomorrow to help fix

[dcherian]

From a quick look maybe we do copy.deepcopy(indexes) in Dataset.copy and pass that to Dataset._replace?

[toddrjen]

My pull request #3871 has a fix already.

[dcherian]

Closed by #3871