Updates to DataTree.equals and DataTree.identical

In contrast to `equals`, `identical` now also checks that any
inherited variables are inherited on both objects. However, they do
not need to be inherited from the same source. This aligns the
behavior of `identical` with the DataTree `__repr__`.

I've also removed the `from_root` argument from `equals` and `identical`.
If a user wants to compare trees from their roots, a better (simpler)
inference is to simply call these methods on the `.root` properties.
I would also like to remove the `strict_names` argument, but that will
require switching to use the new `zip_subtrees` (pydata#9623) first.

xarray/core/datatree.py

@@ -1250,7 +1250,7 @@ def isomorphic(
         except (TypeError, TreeIsomorphismError):
             return False
 
-    def equals(self, other: DataTree, from_root: bool = True) -> bool:
+    def equals(self, other: DataTree) -> bool:
         """
         Two DataTrees are equal if they have isomorphic node structures, with matching node names,
         and if they have matching variables and coordinates, all of which are equal.
@@ -1261,50 +1261,53 @@ def equals(self, other: DataTree, from_root: bool = True) -> bool:
         ----------
         other : DataTree
             The other tree object to compare to.
-        from_root : bool, optional, default is True
-            Whether or not to first traverse to the root of the two trees before checking for isomorphism.
-            If neither tree has a parent then this has no effect.
 
         See Also
         --------
         Dataset.equals
         DataTree.isomorphic
         DataTree.identical
         """
-        if not self.isomorphic(other, from_root=from_root, strict_names=True):
+        if not self.isomorphic(other, strict_names=True):
             return False
 
         return all(
-            [
-                node.dataset.equals(other_node.dataset)
-                for node, other_node in zip(self.subtree, other.subtree, strict=True)
-            ]
+            node.dataset.equals(other_node.dataset)
+            for node, other_node in zip(self.subtree, other.subtree, strict=True)
         )
 
-    def identical(self, other: DataTree, from_root=True) -> bool:
+    def identical(self, other: DataTree) -> bool:
         """
         Like equals, but will also check all dataset attributes and the attributes on
         all variables and coordinates.
 
-        By default this method will check the whole tree above the given node.
-
         Parameters
         ----------
         other : DataTree
             The other tree object to compare to.
-        from_root : bool, optional, default is True
-            Whether or not to first traverse to the root of the two trees before checking for isomorphism.
-            If neither tree has a parent then this has no effect.
 
         See Also
         --------
         Dataset.identical
         DataTree.isomorphic
         DataTree.equals
         """
-        if not self.isomorphic(other, from_root=from_root, strict_names=True):
+        if not self.isomorphic(other, strict_names=True):
+            return False
+
+        if self.name != other.name:
+            return False
+
+        # Check the root node's dataset twice, one with (below) and once without
+        # (here) inheritence. This ensures that even inheritance matches for
+        # identical DataTree objects, although inherited variables need not be
+        # defined at the same level.
+        self_ds = self._to_dataset_view(rebuild_dims=False, inherit=False)
+        other_ds = other._to_dataset_view(rebuild_dims=False, inherit=False)
+        if not self_ds.identical(other_ds):
             return False
 
+        # TODO: switch to zip_subtrees, when available
         return all(
             node.dataset.identical(other_node.dataset)
             for node, other_node in zip(self.subtree, other.subtree, strict=True)

xarray/testing/assertions.py

@@ -3,7 +3,6 @@
 import functools
 import warnings
 from collections.abc import Hashable
-from typing import overload
 
 import numpy as np
 import pandas as pd
@@ -107,16 +106,8 @@ def maybe_transpose_dims(a, b, check_dim_order: bool):
     return b
 
 
-@overload
-def assert_equal(a, b): ...
-
-
-@overload
-def assert_equal(a: DataTree, b: DataTree, from_root: bool = True): ...
-
-
 @ensure_warnings
-def assert_equal(a, b, from_root=True, check_dim_order: bool = True):
+def assert_equal(a, b, check_dim_order: bool = True):
     """Like :py:func:`numpy.testing.assert_array_equal`, but for xarray
     objects.
 
@@ -135,10 +126,6 @@ def assert_equal(a, b, from_root=True, check_dim_order: bool = True):
         or xarray.core.datatree.DataTree. The first object to compare.
     b : xarray.Dataset, xarray.DataArray, xarray.Variable, xarray.Coordinates
         or xarray.core.datatree.DataTree. The second object to compare.
-    from_root : bool, optional, default is True
-        Only used when comparing DataTree objects. Indicates whether or not to
-        first traverse to the root of the trees before checking for isomorphism.
-        If a & b have no parents then this has no effect.
     check_dim_order : bool, optional, default is True
         Whether dimensions must be in the same order.
 
@@ -159,25 +146,13 @@ def assert_equal(a, b, from_root=True, check_dim_order: bool = True):
     elif isinstance(a, Coordinates):
         assert a.equals(b), formatting.diff_coords_repr(a, b, "equals")
     elif isinstance(a, DataTree):
-        if from_root:
-            a = a.root
-            b = b.root
-
-        assert a.equals(b, from_root=from_root), diff_datatree_repr(a, b, "equals")
+        assert a.equals(b), diff_datatree_repr(a, b, "equals")
     else:
         raise TypeError(f"{type(a)} not supported by assertion comparison")
 
 
-@overload
-def assert_identical(a, b): ...
-
-
-@overload
-def assert_identical(a: DataTree, b: DataTree, from_root: bool = True): ...
-
-
 @ensure_warnings
-def assert_identical(a, b, from_root=True):
+def assert_identical(a, b):
     """Like :py:func:`xarray.testing.assert_equal`, but also matches the
     objects' names and attributes.
 
@@ -193,12 +168,6 @@ def assert_identical(a, b, from_root=True):
         The first object to compare.
     b : xarray.Dataset, xarray.DataArray, xarray.Variable or xarray.Coordinates
         The second object to compare.
-    from_root : bool, optional, default is True
-        Only used when comparing DataTree objects. Indicates whether or not to
-        first traverse to the root of the trees before checking for isomorphism.
-        If a & b have no parents then this has no effect.
-    check_dim_order : bool, optional, default is True
-        Whether dimensions must be in the same order.
 
     See Also
     --------
@@ -220,13 +189,7 @@ def assert_identical(a, b, from_root=True):
     elif isinstance(a, Coordinates):
         assert a.identical(b), formatting.diff_coords_repr(a, b, "identical")
     elif isinstance(a, DataTree):
-        if from_root:
-            a = a.root
-            b = b.root
-
-        assert a.identical(b, from_root=from_root), diff_datatree_repr(
-            a, b, "identical"
-        )
+        assert a.identical(b), diff_datatree_repr(a, b, "identical")
     else:
         raise TypeError(f"{type(a)} not supported by assertion comparison")
 

xarray/tests/test_datatree.py

@@ -1529,6 +1529,110 @@ def f(x, tree, y):
         assert actual is dt and actual.attrs == attrs
 
 
+class TestEqualsAndIdentical:
+
+    def test_minimal_variations(self):
+        tree = DataTree.from_dict(
+            {
+                "/": Dataset({"x": 1}),
+                "/child": Dataset({"x": 2}),
+            }
+        )
+        assert tree.equals(tree)
+        assert tree.identical(tree)
+
+        child = tree.children["child"]
+        assert child.equals(child)
+        assert child.identical(child)
+
+        new_child = DataTree(dataset=Dataset({"x": 2}), name="child")
+        assert child.equals(new_child)
+        assert child.identical(new_child)
+
+        anonymous_child = DataTree(dataset=Dataset({"x": 2}))
+        # TODO: re-enable this after fixing .equals() not to require matching
+        # names on the root node (i.e., after switching to use zip_subtrees)
+        # assert child.equals(anonymous_child)
+        assert not child.identical(anonymous_child)
+
+        different_variables = DataTree.from_dict(
+            {
+                "/": Dataset(),
+                "/other": Dataset({"x": 2}),
+            }
+        )
+        assert not tree.equals(different_variables)
+        assert not tree.identical(different_variables)
+
+        different_root_data = DataTree.from_dict(
+            {
+                "/": Dataset({"x": 4}),
+                "/child": Dataset({"x": 2}),
+            }
+        )
+        assert not tree.equals(different_root_data)
+        assert not tree.identical(different_root_data)
+
+        different_child_data = DataTree.from_dict(
+            {
+                "/": Dataset({"x": 1}),
+                "/child": Dataset({"x": 3}),
+            }
+        )
+        assert not tree.equals(different_child_data)
+        assert not tree.identical(different_child_data)
+
+        different_child_node_attrs = DataTree.from_dict(
+            {
+                "/": Dataset({"x": 1}),
+                "/child": Dataset({"x": 2}, attrs={"foo": "bar"}),
+            }
+        )
+        assert tree.equals(different_child_node_attrs)
+        assert not tree.identical(different_child_node_attrs)
+
+        different_child_variable_attrs = DataTree.from_dict(
+            {
+                "/": Dataset({"x": 1}),
+                "/child": Dataset({"x": ((), 2, {"foo": "bar"})}),
+            }
+        )
+        assert tree.equals(different_child_variable_attrs)
+        assert not tree.identical(different_child_variable_attrs)
+
+        different_name = DataTree.from_dict(
+            {
+                "/": Dataset({"x": 1}),
+                "/child": Dataset({"x": 2}),
+            },
+            name="different",
+        )
+        # TODO: re-enable this after fixing .equals() not to require matching
+        # names on the root node (i.e., after switching to use zip_subtrees)
+        # assert tree.equals(different_name)
+        assert not tree.identical(different_name)
+
+    def test_differently_inherited_coordinates(self):
+        root = DataTree.from_dict(
+            {
+                "/": Dataset(coords={"x": [1, 2]}),
+                "/child": Dataset(),
+            }
+        )
+        child = root.children["child"]
+        assert child.equals(child)
+        assert child.identical(child)
+
+        new_child = DataTree(dataset=Dataset(coords={"x": [1, 2]}), name="child")
+        assert child.equals(new_child)
+        assert not child.identical(new_child)
+
+        deeper_root = DataTree(children={"root": root})
+        grandchild = deeper_root["/root/child"]
+        assert child.equals(grandchild)
+        assert child.identical(grandchild)
+
+
 class TestSubset:
     def test_match(self):
         # TODO is this example going to cause problems with case sensitivity?
@@ -1590,7 +1694,7 @@ def test_isel_siblings(self):
             }
         )
         actual = tree.isel(x=-1)
-        assert_equal(actual, expected)
+        assert_identical(actual, expected)
 
         expected = DataTree.from_dict(
             {
@@ -1599,13 +1703,13 @@ def test_isel_siblings(self):
             }
         )
         actual = tree.isel(x=slice(1))
-        assert_equal(actual, expected)
+        assert_identical(actual, expected)
 
         actual = tree.isel(x=[0])
-        assert_equal(actual, expected)
+        assert_identical(actual, expected)
 
         actual = tree.isel(x=slice(None))
-        assert_equal(actual, tree)
+        assert_identical(actual, tree)
 
     def test_isel_inherited(self):
         tree = DataTree.from_dict(
@@ -1622,15 +1726,15 @@ def test_isel_inherited(self):
             }
         )
         actual = tree.isel(x=-1)
-        assert_equal(actual, expected)
+        assert_identical(actual, expected)
 
         expected = DataTree.from_dict(
             {
                 "/child": xr.Dataset({"foo": 4}),
             }
         )
         actual = tree.isel(x=-1, drop=True)
-        assert_equal(actual, expected)
+        assert_identical(actual, expected)
 
         expected = DataTree.from_dict(
             {
@@ -1639,7 +1743,7 @@ def test_isel_inherited(self):
             }
         )
         actual = tree.isel(x=[0])
-        assert_equal(actual, expected)
+        assert_identical(actual, expected)
 
         actual = tree.isel(x=slice(None))
         assert_equal(actual, tree)

xarray/tests/test_datatree_mapping.py

@@ -264,7 +264,7 @@ def times_ten(ds):
 
         expected = create_test_datatree(modify=lambda ds: 10.0 * ds)["set1"]
         result_tree = times_ten(subtree)
-        assert_equal(result_tree, expected, from_root=False)
+        assert_equal(result_tree, expected)
 
     def test_skip_empty_nodes_with_attrs(self, create_test_datatree):
         # inspired by xarray-datatree GH262