minor fixes

lib/iris/common/metadata.py

@@ -27,18 +27,19 @@
 
 
 __all__ = [
-    "SERVICES_COMBINE",
-    "SERVICES_DIFFERENCE",
-    "SERVICES_EQUAL",
-    "SERVICES",
     "AncillaryVariableMetadata",
     "BaseMetadata",
     "CellMeasureMetadata",
     "CoordMetadata",
     "CubeMetadata",
     "DimCoordMetadata",
     "hexdigest",
+    "metadata_filter",
     "metadata_manager_factory",
+    "SERVICES",
+    "SERVICES_COMBINE",
+    "SERVICES_DIFFERENCE",
+    "SERVICES_EQUAL",
 ]
 
 
@@ -1353,13 +1354,13 @@ def metadata_filter(
 ):
     """
     Filter a collection of objects by their metadata to fit the given metadata
-    criteria. Criteria be one or both of: specific properties / other objects
+    criteria. Criteria can be one or both of: specific properties / other objects
     carrying metadata to be matched.
 
     Args:
 
     * instances
-        An iterable of objects to be filtered.
+        One or more objects to be filtered.
 
     Kwargs:
 
@@ -1408,6 +1409,10 @@ def metadata_filter(
     else:
         obj = item
 
+    # apply de morgan's law for one less logical operation
+    if not (isinstance(instances, str) or isinstance(instances, Iterable)):
+        instances = [instances]
+
     result = instances
 
     if name is not None:
@@ -1449,10 +1454,16 @@ def attr_filter(instance):
 
     if axis is not None:
         axis = axis.upper()
+
+        def get_axis(instance):
+            if hasattr(instance, "axis"):
+                axis = instance.axis.upper()
+            else:
+                axis = guess_coord_axis(instance)
+            return axis
+
         result = [
-            instance
-            for instance in result
-            if guess_coord_axis(instance) == axis
+            instance for instance in result if get_axis(instance) == axis
         ]
 
     if obj is not None:

lib/iris/experimental/ugrid.py

@@ -11,7 +11,7 @@
 """
 
 from abc import ABC, abstractmethod
-from collections import namedtuple
+from collections import Iterable, namedtuple
 from functools import wraps
 
 import dask.array as da
@@ -20,18 +20,18 @@
 from .. import _lazy_data as _lazy
 from ..common.metadata import (
     BaseMetadata,
+    metadata_filter,
     metadata_manager_factory,
     SERVICES,
     SERVICES_COMBINE,
     SERVICES_EQUAL,
     SERVICES_DIFFERENCE,
-    metadata_filter,
 )
 from ..common.lenient import _lenient_service as lenient_service
 from ..common.mixin import CFVariableMixin
 from ..config import get_logger
 from ..coords import _DimensionalMetadata, AuxCoord
-from ..exceptions import CoordinateNotFoundError, ConnectivityNotFoundError
+from ..exceptions import ConnectivityNotFoundError, CoordinateNotFoundError
 from ..util import guess_coord_axis
 
 
@@ -831,14 +831,14 @@ def __init__(
         self,
         topology_dimension,
         node_coords_and_axes,
+        connectivities,
         standard_name=None,
         long_name=None,
         var_name=None,
         units=None,
         attributes=None,
         edge_coords_and_axes=None,
         face_coords_and_axes=None,
-        connectivities=None,
         node_dimension=None,
         edge_dimension=None,
         face_dimension=None,
@@ -874,6 +874,12 @@ def normalise(location, axis):
                 raise ValueError(emsg)
             return f"{location}_{axis}"
 
+        if not isinstance(node_coords_and_axes, Iterable):
+            node_coords_and_axes = [node_coords_and_axes]
+
+        if not isinstance(connectivities, Iterable):
+            connectivities = [connectivities]
+
         kwargs = {}
         for coord, axis in node_coords_and_axes:
             kwargs[normalise("node", axis)] = coord

lib/iris/tests/unit/common/metadata/test_metadata_filter.py

@@ -25,6 +25,13 @@
 
 
 class Test_standard(tests.IrisTest):
+    def test_instances_non_iterable(self):
+        item = Mock()
+        item.name.return_value = "one"
+        result = metadata_filter(item, item="one")
+        self.assertEqual(1, len(result))
+        self.assertIn(item, result)
+
     def test_name(self):
         name_one = Mock()
         name_one.name.return_value = "one"
@@ -101,14 +108,25 @@ def test_invalid_attributes(self):
             attributes="one",
         )
 
-    def test_axis(self):
+    def test_axis__by_guess(self):
+        # see https://docs.python.org/3/library/unittest.mock.html#deleting-attributes
         axis_lon = Mock(standard_name="longitude")
+        del axis_lon.axis
         axis_lat = Mock(standard_name="latitude")
+        del axis_lat.axis
         input_list = [axis_lon, axis_lat]
         result = metadata_filter(input_list, axis="x")
         self.assertIn(axis_lon, result)
         self.assertNotIn(axis_lat, result)
 
+    def test_axis__by_member(self):
+        axis_x = Mock(axis="x")
+        axis_y = Mock(axis="y")
+        input_list = [axis_x, axis_y]
+        result = metadata_filter(input_list, axis="x")
+        self.assertEqual(1, len(result))
+        self.assertIn(axis_x, result)
+
     def test_multiple_args(self):
         coord_one = Mock(__class__=AuxCoord, long_name="one")
         coord_two = Mock(__class__=AuxCoord, long_name="two")