Add inherit=False option to DataTree.copy() (#9628)

* Add inherit=False option to DataTree.copy()

This PR adds a inherit=False option to DataTree.copy, so users can
decide if they want to inherit coordinates from parents or not when
creating a subtree.

The default behavior is `inherit=True`, which is a breaking change from
the current behavior where parent coordinates are dropped (which I
believe should be considered a bug).

* fix typing

* add migration guide note

* ignore typing error

DATATREE_MIGRATION_GUIDE.md

@@ -36,7 +36,8 @@ A number of other API changes have been made, which should only require minor mo
 - The top-level import has changed, from `from datatree import DataTree, open_datatree` to `from xarray import DataTree, open_datatree`. Alternatively you can now just use the `import xarray as xr` namespace convention for everything datatree-related.
 - The `DataTree.ds` property has been changed to `DataTree.dataset`, though `DataTree.ds` remains as an alias for `DataTree.dataset`.
 - Similarly the `ds` kwarg in the `DataTree.__init__` constructor has been replaced by `dataset`, i.e. use `DataTree(dataset=)` instead of `DataTree(ds=...)`.
-- The method `DataTree.to_dataset()` still exists but now has different options for controlling which variables are present on the resulting `Dataset`, e.g. `inherited=True/False`.
+- The method `DataTree.to_dataset()` still exists but now has different options for controlling which variables are present on the resulting `Dataset`, e.g. `inherit=True/False`.
+- `DataTree.copy()` also has a new `inherit` keyword argument for controlling whether or not coordinates defined on parents are copied (only relevant when copying a non-root node).
 - The `DataTree.parent` property is now read-only. To assign a ancestral relationships directly you must instead use the `.children` property on the parent node, which remains settable.
 - Similarly the `parent` kwarg has been removed from the `DataTree.__init__` constuctor.
 - DataTree objects passed to the `children` kwarg in `DataTree.__init__` are now shallow-copied.

xarray/core/datatree.py

@@ -826,19 +826,13 @@ def _replace_node(
 
         self.children = children
 
-    def _copy_node(
-        self: DataTree,
-        deep: bool = False,
-    ) -> DataTree:
-        """Copy just one node of a tree"""
-
-        new_node = super()._copy_node()
-
-        data = self._to_dataset_view(rebuild_dims=False, inherit=False)
+    def _copy_node(self, inherit: bool, deep: bool = False) -> Self:
+        """Copy just one node of a tree."""
+        new_node = super()._copy_node(inherit=inherit, deep=deep)
+        data = self._to_dataset_view(rebuild_dims=False, inherit=inherit)
         if deep:
             data = data.copy(deep=True)
         new_node._set_node_data(data)
-
         return new_node
 
     def get(  # type: ignore[override]
@@ -1159,7 +1153,9 @@ def depth(item) -> int:
                     new_nodes_along_path=True,
                 )
 
-        return obj
+        # TODO: figure out why mypy is raising an error here, likely something
+        # to do with the return type of Dataset.copy()
+        return obj  # type: ignore[return-value]
 
     def to_dict(self) -> dict[str, Dataset]:
         """

xarray/core/treenode.py

@@ -10,6 +10,7 @@
     TypeVar,
 )
 
+from xarray.core.types import Self
 from xarray.core.utils import Frozen, is_dict_like
 
 if TYPE_CHECKING:
@@ -238,10 +239,7 @@ def _post_attach_children(self: Tree, children: Mapping[str, Tree]) -> None:
         """Method call after attaching `children`."""
         pass
 
-    def copy(
-        self: Tree,
-        deep: bool = False,
-    ) -> Tree:
+    def copy(self, *, inherit: bool = True, deep: bool = False) -> Self:
         """
         Returns a copy of this subtree.
 
@@ -254,7 +252,12 @@ def copy(
 
         Parameters
         ----------
-        deep : bool, default: False
+        inherit : bool
+            Whether inherited coordinates defined on parents of this node should
+            also be copied onto the new tree. Only relevant if the `parent` of
+            this node is not yet, and "Inherited coordinates" appear in its
+            repr.
+        deep : bool
             Whether each component variable is loaded into memory and copied onto
             the new object. Default is False.
 
@@ -269,35 +272,27 @@ def copy(
         xarray.Dataset.copy
         pandas.DataFrame.copy
         """
-        return self._copy_subtree(deep=deep)
+        return self._copy_subtree(inherit=inherit, deep=deep)
 
-    def _copy_subtree(
-        self: Tree,
-        deep: bool = False,
-        memo: dict[int, Any] | None = None,
-    ) -> Tree:
+    def _copy_subtree(self, inherit: bool, deep: bool = False) -> Self:
         """Copy entire subtree recursively."""
-
-        new_tree = self._copy_node(deep=deep)
+        new_tree = self._copy_node(inherit=inherit, deep=deep)
         for name, child in self.children.items():
             # TODO use `.children[name] = ...` once #9477 is implemented
-            new_tree._set(name, child._copy_subtree(deep=deep))
-
+            new_tree._set(name, child._copy_subtree(inherit=False, deep=deep))
         return new_tree
 
-    def _copy_node(
-        self: Tree,
-        deep: bool = False,
-    ) -> Tree:
+    def _copy_node(self, inherit: bool, deep: bool = False) -> Self:
         """Copy just one node of a tree"""
         new_empty_node = type(self)()
         return new_empty_node
 
-    def __copy__(self: Tree) -> Tree:
-        return self._copy_subtree(deep=False)
+    def __copy__(self) -> Self:
+        return self._copy_subtree(inherit=True, deep=False)
 
-    def __deepcopy__(self: Tree, memo: dict[int, Any] | None = None) -> Tree:
-        return self._copy_subtree(deep=True, memo=memo)
+    def __deepcopy__(self, memo: dict[int, Any] | None = None) -> Self:
+        del memo  # nodes cannot be reused in a DataTree
+        return self._copy_subtree(inherit=True, deep=True)
 
     def _iter_parents(self: Tree) -> Iterator[Tree]:
         """Iterate up the tree, starting from the current node's parent."""
@@ -693,17 +688,14 @@ def __str__(self) -> str:
         name_repr = repr(self.name) if self.name is not None else ""
         return f"NamedNode({name_repr})"
 
-    def _post_attach(self: AnyNamedNode, parent: AnyNamedNode, name: str) -> None:
+    def _post_attach(self, parent: Self, name: str) -> None:
         """Ensures child has name attribute corresponding to key under which it has been stored."""
         _validate_name(name)  # is this check redundant?
         self._name = name
 
-    def _copy_node(
-        self: AnyNamedNode,
-        deep: bool = False,
-    ) -> AnyNamedNode:
+    def _copy_node(self, inherit: bool, deep: bool = False) -> Self:
         """Copy just one node of a tree"""
-        new_node = super()._copy_node()
+        new_node = super()._copy_node(inherit=inherit, deep=deep)
         new_node._name = self.name
         return new_node
 

xarray/tests/test_datatree.py

@@ -414,10 +414,18 @@ def test_copy_coord_inheritance(self) -> None:
         tree = DataTree.from_dict(
             {"/": xr.Dataset(coords={"x": [0, 1]}), "/c": DataTree()}
         )
-        tree2 = tree.copy()
-        node_ds = tree2.children["c"].to_dataset(inherit=False)
+        actual = tree.copy()
+        node_ds = actual.children["c"].to_dataset(inherit=False)
         assert_identical(node_ds, xr.Dataset())
 
+        actual = tree.children["c"].copy()
+        expected = DataTree(Dataset(coords={"x": [0, 1]}), name="c")
+        assert_identical(expected, actual)
+
+        actual = tree.children["c"].copy(inherit=False)
+        expected = DataTree(name="c")
+        assert_identical(expected, actual)
+
     def test_deepcopy(self, create_test_datatree):
         dt = create_test_datatree()