make .parent read-only, and remove tests which test the parent setter

xarray/core/datatree.py

@@ -500,12 +500,6 @@ def parent(self: DataTree) -> DataTree | None:
         """Parent of this node."""
         return self._parent
 
-    @parent.setter
-    def parent(self: DataTree, new_parent: DataTree) -> None:
-        if new_parent and self.name is None:
-            raise ValueError("Cannot set an unnamed node as a child of another node")
-        self._set_parent(new_parent, self.name)
-
     def _to_dataset_view(self, rebuild_dims: bool) -> DatasetView:
         variables = dict(self._data_variables)
         variables |= self._coord_variables
@@ -894,7 +888,7 @@ def _set(self, key: str, val: DataTree | CoercibleValue) -> None:
             # create and assign a shallow copy here so as not to alter original name of node in grafted tree
             new_node = val.copy(deep=False)
             new_node.name = key
-            new_node.parent = self
+            new_node._set_parent(new_parent=self, child_name=key)
         else:
             if not isinstance(val, DataArray | Variable):
                 # accommodate other types that can be coerced into Variables

xarray/core/treenode.py

@@ -86,6 +86,12 @@ def parent(self) -> Tree | None:
         """Parent of this node."""
         return self._parent
 
+    @parent.setter
+    def parent(self: Tree, new_parent: Tree) -> None:
+        raise AttributeError(
+            "Cannot set parent attribute directly, you must modify the children attribute of the other node instead"
+        )
+
     def _set_parent(
         self, new_parent: Tree | None, child_name: str | None = None
     ) -> None:

xarray/tests/test_datatree.py

@@ -35,25 +35,12 @@ def test_bad_names(self):
 
 
 class TestFamilyTree:
-    def test_dont_modify_parent_inplace(self):
-        # GH issue 9196
-        root: DataTree = DataTree(name="root")
-        child: DataTree = DataTree(name="child")
-        child.parent = root
-        assert root.children == {}
-
     def test_dont_modify_children_inplace(self):
         # GH issue 9196
         child: DataTree = DataTree()
         DataTree(children={"child": child})
         assert child.parent is None
 
-    def test_setparent_unnamed_child_node_fails(self):
-        john: DataTree = DataTree(name="john")
-        with pytest.raises(ValueError, match="unnamed"):
-            child = DataTree(name=None)
-            child.parent = john
-
     def test_create_two_children(self):
         root_data = xr.Dataset({"a": ("y", [6, 7, 8]), "set0": ("x", [9, 10])})
         set1_data = xr.Dataset({"a": 0, "b": 1})