Improved Aux factory error handling: better message, delivered earlier (#3182)

* Tests for expected behaviour

* Raise error if aux factory relies on a coordinate external to cube

* Include coordinate name in error message

* Don't check whether dependencies that are "None" are in the coords.

* Review changes: check cube name in error and variable rename

* Truncated variable for flake8

Author: hdyson

lib/iris/cube.py

@@ -994,6 +994,12 @@ def add_aux_factory(self, aux_factory):
         if not isinstance(aux_factory, iris.aux_factory.AuxCoordFactory):
             raise TypeError('Factory must be a subclass of '
                             'iris.aux_factory.AuxCoordFactory.')
+        cube_coords = self.coords()
+        for dependency in aux_factory.dependencies:
+            ref_coord = aux_factory.dependencies[dependency]
+            if ref_coord is not None and ref_coord not in cube_coords:
+                msg = "{} coordinate for factory is not present on cube {}"
+                raise ValueError(msg.format(ref_coord.name(), self.name()))
         self._aux_factories.append(aux_factory)
 
     def add_cell_measure(self, cell_measure, data_dims=None):

lib/iris/tests/unit/cube/test_Cube.py

@@ -34,9 +34,9 @@
 import iris.aux_factory
 import iris.coords
 import iris.exceptions
-from iris import FUTURE
 from iris.analysis import WeightedAggregator, Aggregator
 from iris.analysis import MEAN
+from iris.aux_factory import HybridHeightFactory
 from iris.cube import Cube
 from iris.coords import AuxCoord, DimCoord, CellMeasure
 from iris.exceptions import (CoordinateNotFoundError, CellMeasureNotFoundError,
@@ -1546,6 +1546,31 @@ def test_add_cell_measure(self):
         cube.add_cell_measure(a_cell_measure, [0, 1])
         self.assertEqual(cube.cell_measure('area'), a_cell_measure)
 
+    def test_add_valid_aux_factory(self):
+        cube = Cube(np.arange(8).reshape(2, 2, 2))
+        delta = AuxCoord(points=[0, 1], long_name='delta', units='m')
+        sigma = AuxCoord(points=[0, 1], long_name='sigma')
+        orog = AuxCoord(np.arange(4).reshape(2, 2), units='m')
+        cube.add_aux_coord(delta, 0)
+        cube.add_aux_coord(sigma, 0)
+        cube.add_aux_coord(orog, (1, 2))
+        factory = HybridHeightFactory(delta=delta, sigma=sigma, orography=orog)
+        self.assertIsNone(cube.add_aux_factory(factory))
+
+    def test_error_for_add_invalid_aux_factory(self):
+        cube = Cube(np.arange(8).reshape(2, 2, 2), long_name='bar')
+        delta = AuxCoord(points=[0, 1], long_name='delta', units='m')
+        sigma = AuxCoord(points=[0, 1], long_name='sigma')
+        orog = AuxCoord(np.arange(4).reshape(2, 2), units='m', long_name='foo')
+        cube.add_aux_coord(delta, 0)
+        cube.add_aux_coord(sigma, 0)
+        # Note orography is not added to the cube here
+        factory = HybridHeightFactory(delta=delta, sigma=sigma, orography=orog)
+        expected_error = ("foo coordinate for factory is not present on cube "
+                          "bar")
+        with self.assertRaisesRegexp(ValueError, expected_error):
+            cube.add_aux_factory(factory)
+
 
 class Test_remove_metadata(tests.IrisTest):
     def setUp(self):