Return a copy from get_index

doc/whats-new.rst

@@ -114,6 +114,10 @@ Bug Fixes
   type error when applying reduction methods, due to the reduction methods being
   dynamically generated (:issue:`8136`).
   By `Andrew Scherer <https://github.com/andrew-s28>`_.
+- :py:meth:`DataArray.get_index` and :py:meth:`Dataset.get_index` now return a
+  shallow copy of the stored index, so setting ``.name`` on the result no longer
+  renames the coordinate of the object it came from (:issue:`2949`).
+  By `Chirag Gupta <https://github.com/chiruu12>`_.
 
 .. _`pandas-dev/pandas#64793`: https://github.com/pandas-dev/pandas/pull/64793
 

xarray/core/common.py

@@ -508,7 +508,11 @@ def get_index(self, key: Hashable) -> pd.Index:
             raise KeyError(key)
 
         try:
-            return self._indexes[key].to_pandas_index()
+            # Shallow copy so that renaming the returned index, which pandas
+            # allows in place, cannot reach back into this object's own index.
+            # It shares the underlying data, and xarray already relies on that
+            # being free (see IndexVariable._to_index).
+            return self._indexes[key].to_pandas_index().copy(deep=False)
         except KeyError:
             return pd.Index(range(self.sizes[key]), name=key)
 

xarray/tests/test_dataarray.py

@@ -200,6 +200,17 @@ def test_get_index(self) -> None:
         with pytest.raises(KeyError):
             array.get_index("z")
 
+    def test_get_index_is_not_a_view_of_the_stored_index(self) -> None:
+        # GH2949: a pandas index lets its name be set in place, so handing out
+        # the stored object let a caller rename this array's own coordinate.
+        array = DataArray(np.zeros(2), coords={"x": ["a", "b"]}, dims=["x"])
+
+        array.get_index("x").name = "renamed"
+        array.to_index().name = "renamed too"
+        array.to_series().index.name = "and again"
+
+        assert array.get_index("x").name == "x"
+
     def test_get_index_size_zero(self) -> None:
         array = DataArray(np.zeros((0,)), dims=["x"])
         actual = array.get_index("x")

xarray/tests/test_dataset.py

@@ -778,6 +778,15 @@ def test_asarray(self) -> None:
         with pytest.raises(TypeError, match=r"cannot directly convert"):
             np.asarray(ds)
 
+    def test_get_index_is_not_a_view_of_the_stored_index(self) -> None:
+        # GH2949, the Dataset half: get_index is inherited from
+        # DataWithCoords, so Dataset handed out the stored index too.
+        ds = Dataset({"v": ("x", np.zeros(2))}, coords={"x": ["a", "b"]})
+
+        ds.get_index("x").name = "renamed"
+
+        assert ds.get_index("x").name == "x"
+
     def test_get_index(self) -> None:
         ds = Dataset({"foo": (("x", "y"), np.zeros((2, 3)))}, coords={"x": ["a", "b"]})
         assert ds.get_index("x").equals(pd.Index(["a", "b"]))