update using dictionary unpacking (#213)

* merge two dictionaries using dictionary unpacking

* check that the fix actually worked

* use `|` to combine two dictionaries

* Revert "use `|` to combine two dictionaries"

This reverts commit ecfbbd5.

---------

Co-authored-by: Tom Nicholas <[email protected]>

Author: keewis

datatree/datatree.py

@@ -878,7 +878,7 @@ def update(self, other: Dataset | Mapping[str, DataTree | DataArray]) -> None:
 
         vars_merge_result = dataset_update_method(self.to_dataset(), new_variables)
         # TODO are there any subtleties with preserving order of children like this?
-        merged_children = OrderedDict(**self.children, **new_children)
+        merged_children = OrderedDict({**self.children, **new_children})
         self._replace(
             inplace=True, children=merged_children, **vars_merge_result._asdict()
         )

datatree/tests/test_datatree.py

@@ -235,6 +235,17 @@ def test_update_doesnt_alter_child_name(self):
         child = dt["a"]
         assert child.name == "a"
 
+    def test_update_overwrite(self):
+        actual = DataTree.from_dict({"a": DataTree(xr.Dataset({"x": 1}))})
+        actual.update({"a": DataTree(xr.Dataset({"x": 2}))})
+
+        expected = DataTree.from_dict({"a": DataTree(xr.Dataset({"x": 2}))})
+
+        print(actual)
+        print(expected)
+
+        dtt.assert_equal(actual, expected)
+
 
 class TestCopy:
     def test_copy(self, create_test_datatree):