Make illegal path-like variable names when constructing a DataTree from a Dataset

doc/whats-new.rst

@@ -37,6 +37,9 @@ Deprecations
 Bug fixes
 ~~~~~~~~~
 
+- Make illegal path-like variable names when constructing a DataTree from a Dataset
+  (:issue:`9339`, :pull:`9378`)
+  By `Etienne Schalk <https://github.com/etienneschalk>`_.
 - Fix bug with rechunking to a frequency when some periods contain no data (:issue:`9360`).
   By `Deepak Cherian <https://github.com/dcherian>`_.
 - Fix bug causing `DataTree.from_dict` to be sensitive to insertion order (:issue:`9276`, :pull:`9292`).

xarray/core/datatree.py

@@ -158,6 +158,18 @@ def _check_alignment(
             _check_alignment(child_path, child_ds, base_ds, child.children)
 
 
+def _check_for_slashes_in_names(variables: Iterable[Hashable]) -> None:
+    offending_variable_names = [
+        name for name in variables if isinstance(name, str) and "/" in name
+    ]
+    if len(offending_variable_names) > 0:
+        raise KeyError(
+            f"Given Dataset contains path-like variable names: {offending_variable_names}. "
+            "A Dataset represents a group, and a single group "
+            "cannot have path-like variable names. "
+        )
+
+
 class DatasetView(Dataset):
     """
     An immutable Dataset-like view onto the data in a single DataTree node.
@@ -459,7 +471,9 @@ def __init__(
             children = {}
 
         super().__init__(name=name)
-        self._set_node_data(_coerce_to_dataset(data))
+        ds = _coerce_to_dataset(data)
+        self._set_node_data(ds)
+        _check_for_slashes_in_names(ds.variables)
         self.parent = parent
         self.children = children
 

xarray/tests/test_datatree.py

@@ -72,6 +72,23 @@ def test_child_gets_named_on_attach(self):
         mary: DataTree = DataTree(children={"Sue": sue})  # noqa
         assert sue.name == "Sue"
 
+    def test_dataset_containing_slashes(self):
+        xda: xr.DataArray = xr.DataArray(
+            [[1, 2]],
+            coords={"label": ["a"], "R30m/y": [30, 60]},
+        )
+        xds: xr.Dataset = xr.Dataset({"group/subgroup/my_variable": xda})
+        with pytest.raises(
+            KeyError,
+            match=re.escape(
+                "Given Dataset contains path-like variable names: "
+                "['R30m/y', 'group/subgroup/my_variable']. "
+                "A Dataset represents a group, and a single group cannot "
+                "have path-like variable names. "
+            ),
+        ):
+            DataTree(xds)
+
 
 class TestPaths:
     def test_path_property(self):