Forbid pathlike DataTree coordinate names

doc/whats-new.rst

@@ -29,12 +29,17 @@ Bug Fixes
 - Ensure that ``keep_attrs='drop'`` and ``keep_attrs=False`` remove attrs from result, even when there is
   only one xarray object given to ``apply_ufunc`` (:issue:`10982` :pull:`10997`).
   By `Julia Signell <https://github.com/jsignell>`_.
+- Forbid slashes in ``DataTree`` coordinate names (:issue:`#9485` :pull:`11015`).
+  By `Ewan Short <https://github.com/eshort0401>`_.
 
 Documentation
 ~~~~~~~~~~~~~
 
 - Better description of ``keep_attrs`` option on ``xarray.where`` docstring (:issue:`10982` :pull:`10997`).
   By `Julia Signell <https://github.com/jsignell>`_.
+- Clarify ``DataTree.coords`` and ``DataTree.data_vars`` docstrings to indicate
+they refer to the coordinates and variables of that node only (:issue:`9485` :pull:`11015`).
+  By `Ewan Short <https://github.com/eshort0401>`_.
 
 Internal Changes
 ~~~~~~~~~~~~~~~~

xarray/core/coordinates.py

@@ -1019,6 +1019,11 @@ def _update_coords(
     ) -> None:
         from xarray.core.datatree import check_alignment
 
+        # For now, ensure coordinate keys do not contain '/' character. See
+        # https://github.com/pydata/xarray/issues/9485
+        # https://github.com/pydata/xarray/pull/9492
+        _validate_coordinate_names(coords.keys())
+
         # create updated node (`.to_dataset` makes a copy so this doesn't modify in-place)
         node_ds = self._data.to_dataset(inherit=False)
         node_ds.coords._update_coords(coords, indexes)
@@ -1060,6 +1065,19 @@ def _ipython_key_completions_(self):
         ]
 
 
+def _validate_coordinate_names(coordinates: Iterable[Hashable]) -> None:
+    offending_coordinate_names = [
+        name for name in coordinates if isinstance(name, str) and "/" in name
+    ]
+    if len(offending_coordinate_names) > 0:
+        raise ValueError(
+            "Given coordinate names contain the '/' character: "
+            f"{offending_coordinate_names}. Accessing the coordinates of other nodes "
+            "in the tree is not yet supported here. Retrieve the other node first, "
+            "then access its coordinates."
+        )
+
+
 class DataArrayCoordinates(Coordinates, Generic[T_DataArray]):
     """Dictionary like container for DataArray coordinates (variables + indexes).
 

xarray/core/datatree.py

@@ -1467,13 +1467,14 @@ def xindexes(self) -> Indexes[Index]:
     @property
     def coords(self) -> DataTreeCoordinates:
         """Dictionary of xarray.DataArray objects corresponding to coordinate
-        variables
+        variables at this node.
         """
         return DataTreeCoordinates(self)
 
     @property
     def data_vars(self) -> DataVariables:
-        """Dictionary of DataArray objects corresponding to data variables"""
+        """Dictionary of DataArray objects corresponding to data variables at this
+        node."""
         return DataVariables(self.to_dataset())
 
     def isomorphic(self, other: DataTree) -> bool:

xarray/tests/test_datatree.py

@@ -762,6 +762,23 @@ def test_inherited(self) -> None:
         # expected = child.assign_coords({"c": 11})
         # assert_identical(expected, actual)
 
+    def test_forbid_access_other_node_coords(self) -> None:
+        ds = Dataset(coords={"x": 0})
+        tree = DataTree(ds, children={"child": DataTree()})
+        expected = DataTree(ds, children={"child": DataTree(Dataset(coords={"y": 2}))})
+        with pytest.raises(
+            ValueError,
+            match=re.escape(
+                "Given coordinate names contain the '/' character: ['/child/y']. "
+                "Accessing the coordinates of other nodes in the tree is not yet "
+                "supported here. Retrieve the other node first, then access its "
+                "coordinates."
+            ),
+        ):
+            tree.coords["/child/y"] = 2
+        tree["child"].coords["y"] = DataArray(2)
+        assert_equal(tree, expected)
+
 
 def test_delitem() -> None:
     ds = Dataset({"a": 0}, coords={"x": ("x", [1, 2]), "z": "a"})