Fix PP callback bug

lib/iris/fileformats/rules.py

@@ -950,7 +950,7 @@ def _resolve_factory_references(cube, factories, concrete_reference_targets,
 
 
 def _load_pairs_from_fields_and_filenames(fields_and_filenames, converter,
-                                          user_callback=None):
+                                          user_callback_wrapper=None):
     # The underlying mechanism for the public 'load_pairs_from_fields' and
     # 'load_cubes'.
     # Slightly more complicated than 'load_pairs_from_fields', only because it
@@ -962,10 +962,14 @@ def _load_pairs_from_fields_and_filenames(fields_and_filenames, converter,
         cube, factories, references = _make_cube(field, converter)
 
         # Post modify the new cube with a user-callback.
-        # This an ordinary Iris load callback, so it takes the filename.
-        cube = iris.io.run_callback(user_callback, cube, field, filename)
-
-        # Cross referencing
+        # This is an ordinary Iris load callback, so it takes the filename.
+        cube = iris.io.run_callback(user_callback_wrapper,
+                                    cube, field, filename)
+        # Callback mechanism may return None, which must not be yielded.
+        if cube is None:
+            continue
+
+        # Cross referencing.
         for reference in references:
             name = reference.name
             # Register this cube as a source cube for the named reference.
@@ -1017,7 +1021,7 @@ def load_cubes(filenames, user_callback, loader, filter_function=None):
     def _generate_all_fields_and_filenames():
         for filename in filenames:
             for field in loader.field_generator(
-                filename, **loader.field_generator_kwargs):
+                    filename, **loader.field_generator_kwargs):
                 # evaluate field against format specific desired attributes
                 # load if no format specific desired attributes are violated
                 if filter_function is None or filter_function(field):
@@ -1031,13 +1035,15 @@ def loadcubes_user_callback_wrapper(cube, field, filename):
             loader.legacy_custom_rules.verify(cube, field)
 
         # Then also run user-provided original callback function.
-        cube = iris.io.run_callback(user_callback, cube, field, filename)
-        return cube
+        result = cube
+        if user_callback is not None:
+            result = user_callback(cube, field, filename)
+        return result
 
     all_fields_and_filenames = _generate_all_fields_and_filenames()
     for cube, field in _load_pairs_from_fields_and_filenames(
             all_fields_and_filenames,
             converter=loader.converter,
-            user_callback=loadcubes_user_callback_wrapper):
+            user_callback_wrapper=loadcubes_user_callback_wrapper):
         yield cube
 

lib/iris/tests/integration/test_pp.py

@@ -31,6 +31,7 @@
 from iris.cube import Cube
 import iris.fileformats.pp
 import iris.fileformats.pp_rules
+from iris.exceptions import IgnoreCubeException
 from iris.tests import mock
 from iris.fileformats.pp import load_pairs_from_fields
 
@@ -636,5 +637,27 @@ def test_time_mean_and_zonal_mean(self):
         self.assertEqual(int(field.lbproc), 192)
 
 
+class TestCallbackLoad(tests.IrisTest):
+    def setUp(self):
+        self.pass_name = 'air_potential_temperature'
+
+    def callback_wrapper(self):
+        # Wrap the `iris.exceptions.IgnoreCubeException`-calling callback.
+        def callback_ignore_cube_exception(cube, field, filename):
+            if cube.name() != self.pass_name:
+                raise IgnoreCubeException
+        return callback_ignore_cube_exception
+
+    def test_ignore_cube_callback(self):
+        test_dataset = tests.get_data_path(
+            ['PP', 'globClim1', 'dec_subset.pp'])
+        exception_callback = self.callback_wrapper()
+        result_cubes = iris.load(test_dataset, callback=exception_callback)
+        n_result_cubes = len(result_cubes)
+        # We ignore all but one cube (the `air_potential_temperature` cube).
+        self.assertEqual(n_result_cubes, 1)
+        self.assertEqual(result_cubes[0].name(), self.pass_name)
+
+
 if __name__ == "__main__":
     tests.main()