Do not change coordinate inplace when throwing error (pydata#5957)

Author: gcaria

xarray/core/dataset.py

@@ -224,6 +224,7 @@ def merge_indexes(
     vars_to_remove: List[Hashable] = []
     dims_to_replace: Dict[Hashable, Hashable] = {}
     error_msg = "{} is not the name of an existing variable."
+    keep_attrs = _get_keep_attrs(default=True)
 
     for dim, var_names in indexes.items():
         if isinstance(var_names, str) or not isinstance(var_names, Sequence):
@@ -277,7 +278,8 @@ def merge_indexes(
             for n in names:
                 dims_to_replace[n] = dim
 
-        vars_to_replace[dim] = IndexVariable(dim, idx)
+        attrs = variables[var_names[0]].attrs if keep_attrs else None
+        vars_to_replace[dim] = IndexVariable(dim, idx, attrs=attrs)
         vars_to_remove.extend(var_names)
 
     new_variables = {k: v for k, v in variables.items() if k not in vars_to_remove}

xarray/core/variable.py

@@ -2813,6 +2813,11 @@ def name(self):
     def name(self, value):
         raise AttributeError("cannot modify name of IndexVariable in-place")
 
+    def _inplace_binary_op(self, other, f):
+        raise TypeError(
+            "Values of an IndexVariable are immutable and can not be modified inplace"
+        )
+
 
 # for backwards compatibility
 Coordinate = utils.alias(IndexVariable, "Coordinate")

xarray/tests/test_dataarray.py

@@ -1987,6 +1987,18 @@ def test_inplace_math_basics(self):
         assert_array_equal(b.values, x)
         assert source_ndarray(b.values) is x
 
+    def test_inplace_math_error(self):
+        data = np.random.rand(4)
+        times = np.arange(4)
+        foo = DataArray(data, coords=[times], dims=["time"])
+        b = times.copy()
+        with pytest.raises(
+            TypeError, match=r"Values of an IndexVariable are immutable"
+        ):
+            foo.coords["time"] += 1
+        # Check error throwing prevented inplace operation
+        assert_array_equal(foo.coords["time"], b)
+
     def test_inplace_math_automatic_alignment(self):
         a = DataArray(range(5), [("x", range(5))])
         b = DataArray(range(1, 6), [("x", range(1, 6))])

xarray/tests/test_dataset.py

@@ -2976,6 +2976,15 @@ def test_set_index(self):
             ds.set_index(foo="bar")
         assert str(excinfo.value) == "bar is not the name of an existing variable."
 
+        # ensure attrs are kept
+        da = DataArray([1, 2], dims=["x"])
+        da.coords["x"] = (["x"], [2, 3], {"name": "coord_1"})
+        da.coords["a"] = (["x"], [0, 1], {"name": "coord_2"})
+        ds = Dataset({"x_var": da})
+        assert ds.set_index(x="a").x.attrs == {"name": "coord_2"}
+        with set_options(keep_attrs=False):
+            assert ds.set_index(x="a").x.attrs == {}
+
     def test_reset_index(self):
         ds = create_test_multiindex()
         mindex = ds["x"].to_index()

xarray/tests/test_variable.py

@@ -1656,6 +1656,14 @@ def test_inplace_math(self):
         with pytest.raises(ValueError, match=r"dimensions cannot change"):
             v += Variable("y", np.arange(5))
 
+    def test_inplace_math_error(self):
+        x = np.arange(5)
+        v = IndexVariable(["x"], x)
+        with pytest.raises(
+            TypeError, match=r"Values of an IndexVariable are immutable"
+        ):
+            v += 1
+
     def test_reduce(self):
         v = Variable(["x", "y"], self.d, {"ignored": "attributes"})
         assert_identical(v.reduce(np.std, "x"), Variable(["y"], self.d.std(axis=0)))