Reset output variables: avoid update attrs in original dataset (#101)

* avoid update attrs in original dataset

* update release notes

doc/whats_new.rst

@@ -72,6 +72,8 @@ Bug fixes
 
 - Remove ``attrs`` 19.2.0 depreciation warning (:issue:`68`).
 - Fix compatibility with xarray 0.14.1 (:issue:`69`).
+- Avoid update in-place attributes in original/input xarray Datasets
+  (:issue:`101`).
 
 v0.3.0 (30 September 2019)
 --------------------------

xsimlab/tests/fixture_model.py

@@ -158,7 +158,7 @@ def in_dataset():
     )
 
     ds["clock"].attrs[svars_key] = "profile__u"
-    ds["out"].attrs[svars_key] = "roll__u_diff," "add__u_diff"
+    ds["out"].attrs[svars_key] = "roll__u_diff,add__u_diff"
     ds.attrs[svars_key] = "profile__u_opp"
 
     return ds

xsimlab/tests/test_xr_accessor.py

@@ -248,6 +248,10 @@ def test_filter_vars(self, simple_model, in_dataset):
         assert sorted(filtered_ds.xsimlab.clock_coords) == ["clock", "out"]
         assert filtered_ds.out.attrs[self._output_vars_key] == "roll__u_diff"
 
+        # test unchanged attributes in original dataset
+        assert in_dataset.out.attrs[self._output_vars_key] == "roll__u_diff,add__u_diff"
+        assert in_dataset.attrs[self._output_vars_key] == "profile__u_opp"
+
     def test_set_output_vars(self, model):
         ds = xr.Dataset()
         ds["clock"] = (

xsimlab/xr_accessor.py

@@ -250,6 +250,26 @@ def _set_input_vars(self, model, input_vars):
 
             self._ds[xr_var_name] = xr_var
 
+    def _set_output_vars_attr(self, clock, value):
+        # avoid update attrs in original dataset
+
+        if clock is None:
+            attrs = self._ds.attrs.copy()
+        else:
+            attrs = self._ds[clock].attrs.copy()
+
+        if value is None:
+            attrs.pop(self._output_vars_key, None)
+        else:
+            attrs[self._output_vars_key] = value
+
+        if clock is None:
+            self._ds.attrs = attrs
+        else:
+            new_coord = self._ds.coords[clock].copy()
+            new_coord.attrs = attrs
+            self._ds[clock] = new_coord
+
     def _set_output_vars(self, model, output_vars, clear=False):
         # TODO: remove this ugly code (depreciated output_vars format)
         o_vars = {}
@@ -297,18 +317,13 @@ def _set_output_vars(self, model, output_vars, clear=False):
 
         for clock, var_list in clock_vars.items():
             var_str = ",".join(var_list)
-
-            if clock is None:
-                self._ds.attrs[self._output_vars_key] = var_str
-            else:
-                coord = self.clock_coords[clock]
-                coord.attrs[self._output_vars_key] = var_str
+            self._set_output_vars_attr(clock, var_str)
 
     def _reset_output_vars(self, model, output_vars):
-        self._ds.attrs.pop(self._output_vars_key, None)
+        self._set_output_vars_attr(None, None)
 
-        for coord in self.clock_coords.values():
-            coord.attrs.pop(self._output_vars_key, None)
+        for clock in self.clock_coords:
+            self._set_output_vars_attr(clock, None)
 
         self._set_output_vars(model, output_vars, clear=True)