BUG: Tolerant crs comparison

lib/iris/coord_systems.py

@@ -31,6 +31,30 @@
 import cartopy.crs as ccrs
 
 
+def _dict_nearly_equal(dict1, dict2):
+    # Allow coordinate system comparison (floating point numbers with
+    # tolerance).
+    for key, value in dict1.iteritems():
+        if key not in dict2:
+            result = False
+            break
+        if hasattr(dict2[key], '__dict__') and hasattr(value, '__dict__'):
+            result = _dict_nearly_equal(dict2[key].__dict__,
+                                        value.__dict__)
+        elif hasattr(dict2[key], '__dict__') != hasattr(value, '__dict__'):
+            result = False
+        else:
+            # We intentionally do not use a global tolerance for coordinate
+            # system comparison.
+            try:
+                result = np.allclose(dict2[key], value, 1e-5)
+            except (TypeError, ValueError):
+                result = dict2[key] == value
+        if not result:
+            break
+    return result
+
+
 class CoordSystem(six.with_metaclass(ABCMeta, object)):
     """
     Abstract base class for coordinate systems.
@@ -40,8 +64,10 @@ class CoordSystem(six.with_metaclass(ABCMeta, object)):
     grid_mapping_name = None
 
     def __eq__(self, other):
-        return (self.__class__ == other.__class__ and
-                self.__dict__ == other.__dict__)
+        res = False
+        if other is not None:
+            res = _dict_nearly_equal(self.__dict__, other.__dict__)
+        return res
 
     def __ne__(self, other):
         # Must supply __ne__, Python does not defer to __eq__ for

lib/iris/tests/unit/coord_systems/test_GeogCS.py

@@ -0,0 +1,79 @@
+# (C) British Crown Copyright 2016, Met Office
+#
+# This file is part of Iris.
+#
+# Iris is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Iris is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with Iris.  If not, see <http://www.gnu.org/licenses/>.
+"""Unit tests for the :class:`iris.coord_systems.GeogCS` class."""
+
+from __future__ import (absolute_import, division, print_function)
+from six.moves import (filter, input, map, range, zip)  # noqa
+
+# Import iris.tests first so that some things can be initialised before
+# importing anything else.
+import iris.tests as tests
+
+import numpy as np
+
+from iris.coord_systems import GeogCS
+
+
+class Test___eq__(tests.IrisTest):
+    def test_derived_quantities_eq(self):
+        # Ensure that derived quantities are equal.
+        crs1 = GeogCS(semi_major_axis=6377563.396, semi_minor_axis=6356256.909)
+        crs2 = GeogCS(semi_major_axis=6377563.396,
+                      inverse_flattening=299.324)
+        self.assertEqual(crs1, crs2)
+
+    def test_32bit_derived_quantities_eq(self):
+        # Ensure that 32-bit coerced quantities don't fail equality.
+        crs1 = GeogCS(semi_major_axis=6377563.396, semi_minor_axis=6356256.909)
+        crs2 = GeogCS(semi_major_axis=np.float32(6377563.396),
+                      inverse_flattening=np.float32(299.324))
+        self.assertEqual(crs1, crs2)
+
+    def test_derived_quantities_neq(self):
+        # Ensure that derived quantities are not equal.
+        crs1 = GeogCS(semi_major_axis=6377563.396, semi_minor_axis=6356256.909)
+        crs2 = GeogCS(semi_major_axis=6377563.396,
+                      inverse_flattening=299.33)
+        self.assertFalse(crs1 == crs2)
+
+    def test_straight_eq(self):
+        # No derived quantities.
+        crs1 = GeogCS(6377560)
+        crs2 = GeogCS(6377570)
+        self.assertEqual(crs1, crs2)
+
+    def test_straight_neq(self):
+        # No derived quantities.
+        crs1 = GeogCS(6377500)
+        crs2 = GeogCS(6377600)
+        self.assertFalse(crs1 == crs2)
+
+    def test_straight_32bit_eq(self):
+        # No derived quantities.
+        crs1 = GeogCS(6377560)
+        crs2 = GeogCS(np.float32(6377570))
+        self.assertEqual(crs1, crs2)
+
+    def test_straight_32bit_neq(self):
+        # No derived quantities.
+        crs1 = GeogCS(6377500)
+        crs2 = GeogCS(np.float32(6377600))
+        self.assertFalse(crs1 == crs2)
+
+
+if __name__ == '__main__':
+    tests.main()