Add support for reverse iteration of Choices (#314)

CHANGES.rst

@@ -6,6 +6,7 @@ master (unreleased)
 - Fix handling of deferred attributes on Django 1.10+, fixes GH-278
 - Fix `FieldTracker.has_changed()` and `FieldTracker.previous()` to return
   correct responses for deferred fields.
+- Support `reversed` for all kinds of `Choices` objects, fixes GH-309
 - Fix Model instance non picklable GH-330
 
 3.1.2 (2018.05.09)

model_utils/choices.py

@@ -102,6 +102,9 @@ class Choices(object):
     def __iter__(self):
         return iter(self._doubles)
 
+    def __reversed__(self):
+        return reversed(self._doubles)
+
     def __getattr__(self, attname):
         try:
             return self._identifier_map[attname]

tests/test_choices.py

@@ -16,7 +16,12 @@ class ChoicesTests(TestCase):
         self.assertEqual(self.STATUS['PUBLISHED'], 'PUBLISHED')
 
     def test_iteration(self):
-        self.assertEqual(tuple(self.STATUS), (('DRAFT', 'DRAFT'), ('PUBLISHED', 'PUBLISHED')))
+        self.assertEqual(tuple(self.STATUS),
+                         (('DRAFT', 'DRAFT'), ('PUBLISHED', 'PUBLISHED')))
+
+    def test_reversed(self):
+        self.assertEqual(tuple(reversed(self.STATUS)),
+                         (('PUBLISHED', 'PUBLISHED'), ('DRAFT', 'DRAFT')))
 
     def test_len(self):
         self.assertEqual(len(self.STATUS), 2)
@@ -78,8 +83,15 @@ class LabelChoicesTests(ChoicesTests):
         self.assertEqual(tuple(self.STATUS), (
             ('DRAFT', 'is draft'),
             ('PUBLISHED', 'is published'),
-            ('DELETED', 'DELETED'))
-        )
+            ('DELETED', 'DELETED'),
+        ))
+
+    def test_reversed(self):
+        self.assertEqual(tuple(reversed(self.STATUS)), (
+            ('DELETED', 'DELETED'),
+            ('PUBLISHED', 'is published'),
+            ('DRAFT', 'is draft'),
+        ))
 
     def test_indexing(self):
         self.assertEqual(self.STATUS['PUBLISHED'], 'is published')
@@ -169,7 +181,15 @@ class IdentifierChoicesTests(ChoicesTests):
         self.assertEqual(tuple(self.STATUS), (
             (0, 'is draft'),
             (1, 'is published'),
-            (2, 'is deleted')))
+            (2, 'is deleted'),
+        ))
+
+    def test_reversed(self):
+        self.assertEqual(tuple(reversed(self.STATUS)), (
+            (2, 'is deleted'),
+            (1, 'is published'),
+            (0, 'is draft'),
+        ))
 
     def test_indexing(self):
         self.assertEqual(self.STATUS[1], 'is published')