Don't realise lazy coords in netcdf save.

lib/iris/fileformats/netcdf.py

@@ -1190,9 +1190,9 @@ def write(
 
         # Ensure that attributes are CF compliant and if possible to make them
         # compliant.
-        self.check_attribute_compliance(cube, cube.lazy_data())
+        self.check_attribute_compliance(cube, cube.dtype)
         for coord in cube.coords():
-            self.check_attribute_compliance(coord, coord.points)
+            self.check_attribute_compliance(coord, coord.dtype)
 
         # Get suitable dimension names.
         mesh_dimensions, cube_dimensions = self._get_dim_names(cube)
@@ -1280,16 +1280,14 @@ def write(
                 warnings.warn(msg)
 
     @staticmethod
-    def check_attribute_compliance(container, data):
+    def check_attribute_compliance(container, data_dtype):
         def _coerce_value(val_attr, val_attr_value, data_dtype):
             val_attr_tmp = np.array(val_attr_value, dtype=data_dtype)
             if (val_attr_tmp != val_attr_value).any():
                 msg = '"{}" is not of a suitable value ({})'
                 raise ValueError(msg.format(val_attr, val_attr_value))
             return val_attr_tmp
 
-        data_dtype = data.dtype
-
         # Ensure that conflicting attributes are not provided.
         if (
             container.attributes.get("valid_min") is not None

lib/iris/tests/integration/test_netcdf.py

@@ -273,10 +273,16 @@ def test_lazy_preserved_save(self):
         )
         acube = iris.load_cube(fpath, "air_temperature")
         self.assertTrue(acube.has_lazy_data())
+        # Also check a coord with lazy points + bounds.
+        self.assertTrue(acube.coord("forecast_period").has_lazy_points())
+        self.assertTrue(acube.coord("forecast_period").has_lazy_bounds())
         with self.temp_filename(".nc") as nc_path:
             with Saver(nc_path, "NETCDF4") as saver:
                 saver.write(acube)
+        # Check that cube data is not realised, also coord points + bounds.
         self.assertTrue(acube.has_lazy_data())
+        self.assertTrue(acube.coord("forecast_period").has_lazy_points())
+        self.assertTrue(acube.coord("forecast_period").has_lazy_bounds())
 
 
 @tests.skip_data

lib/iris/tests/unit/fileformats/netcdf/test_Saver.py

@@ -612,7 +612,7 @@ class _Common__check_attribute_compliance:
 
     def setUp(self):
         self.container = mock.Mock(name="container", attributes={})
-        self.data = self.array_lib.array(1, dtype="int32")
+        self.data_dtype = np.dtype("int32")
 
         patch = mock.patch("netCDF4.Dataset")
         _ = patch.start()
@@ -629,7 +629,7 @@ def assertAttribute(self, value):
     def check_attribute_compliance_call(self, value):
         self.set_attribute(value)
         with Saver(mock.Mock(), "NETCDF4") as saver:
-            saver.check_attribute_compliance(self.container, self.data)
+            saver.check_attribute_compliance(self.container, self.data_dtype)
 
 
 class Test_check_attribute_compliance__valid_range(
@@ -642,10 +642,10 @@ def attribute(self):
     def test_valid_range_type_coerce(self):
         value = self.array_lib.array([1, 2], dtype="float")
         self.check_attribute_compliance_call(value)
-        self.assertAttribute(self.data.dtype)
+        self.assertAttribute(self.data_dtype)
 
     def test_valid_range_unsigned_int8_data_signed_range(self):
-        self.data = self.data.astype("uint8")
+        self.data_dtype = np.dtype("uint8")
         value = self.array_lib.array([1, 2], dtype="int8")
         self.check_attribute_compliance_call(value)
         self.assertAttribute(value.dtype)
@@ -658,7 +658,7 @@ def test_valid_range_cannot_coerce(self):
 
     def test_valid_range_not_numpy_array(self):
         # Ensure we handle the case when not a numpy array is provided.
-        self.data = self.data.astype("int8")
+        self.data_dtype = np.dtype("int8")
         value = [1, 2]
         self.check_attribute_compliance_call(value)
         self.assertAttribute(np.int64)
@@ -674,10 +674,10 @@ def attribute(self):
     def test_valid_range_type_coerce(self):
         value = self.array_lib.array(1, dtype="float")
         self.check_attribute_compliance_call(value)
-        self.assertAttribute(self.data.dtype)
+        self.assertAttribute(self.data_dtype)
 
     def test_valid_range_unsigned_int8_data_signed_range(self):
-        self.data = self.data.astype("uint8")
+        self.data_dtype = np.dtype("uint8")
         value = self.array_lib.array(1, dtype="int8")
         self.check_attribute_compliance_call(value)
         self.assertAttribute(value.dtype)
@@ -690,7 +690,7 @@ def test_valid_range_cannot_coerce(self):
 
     def test_valid_range_not_numpy_array(self):
         # Ensure we handle the case when not a numpy array is provided.
-        self.data = self.data.astype("int8")
+        self.data_dtype = np.dtype("int8")
         value = 1
         self.check_attribute_compliance_call(value)
         self.assertAttribute(np.int64)
@@ -706,10 +706,10 @@ def attribute(self):
     def test_valid_range_type_coerce(self):
         value = self.array_lib.array(2, dtype="float")
         self.check_attribute_compliance_call(value)
-        self.assertAttribute(self.data.dtype)
+        self.assertAttribute(self.data_dtype)
 
     def test_valid_range_unsigned_int8_data_signed_range(self):
-        self.data = self.data.astype("uint8")
+        self.data_dtype = np.dtype("uint8")
         value = self.array_lib.array(2, dtype="int8")
         self.check_attribute_compliance_call(value)
         self.assertAttribute(value.dtype)
@@ -722,7 +722,7 @@ def test_valid_range_cannot_coerce(self):
 
     def test_valid_range_not_numpy_array(self):
         # Ensure we handle the case when not a numpy array is provided.
-        self.data = self.data.astype("int8")
+        self.data_dtype = np.dtype("int8")
         value = 2
         self.check_attribute_compliance_call(value)
         self.assertAttribute(np.int64)
@@ -733,13 +733,15 @@ class Test_check_attribute_compliance__exception_handling(
 ):
     def test_valid_range_and_valid_min_valid_max_provided(self):
         # Conflicting attributes should raise a suitable exception.
-        self.data = self.data.astype("int8")
+        self.data_dtype = np.dtype("int8")
         self.container.attributes["valid_range"] = [1, 2]
         self.container.attributes["valid_min"] = [1]
         msg = 'Both "valid_range" and "valid_min"'
         with Saver(mock.Mock(), "NETCDF4") as saver:
             with self.assertRaisesRegex(ValueError, msg):
-                saver.check_attribute_compliance(self.container, self.data)
+                saver.check_attribute_compliance(
+                    self.container, self.data_dtype
+                )
 
 
 class Test__cf_coord_identity(tests.IrisTest):

lib/iris/tests/unit/fileformats/netcdf/test_Saver__lazy.py

@@ -122,3 +122,7 @@ def test_lazy_streamed_bounds(self):
         self.cube.replace_coord(lazy_coord)
         self.save_common(self.cube)
         self.assertTrue(self.store_watch.called)
+
+
+if __name__ == "__main__":
+    tests.main()