Fixed bad comparison logic introduced in d97bf2e9.

Refs #21765.

Thanks to kezabelle for the quick report and to onjin
for providing the patch.

django/template/context.py

@@ -102,7 +102,15 @@ class BaseContext(object):
         Compares two contexts by comparing theirs 'dicts' attributes.
         """
         if isinstance(other, BaseContext):
-            return self.dicts[-1] == other.dicts[-1]
+            # because dictionaries can be put in different order
+            # we have to flatten them like in templates
+            def flatten(dicts):
+                flat = {}
+                for d in dicts:
+                    flat.update(d)
+                return flat
+
+            return flatten(self.dicts) == flatten(other.dicts)
 
         # if it's not comparable return false
         return False

tests/template_tests/test_context.py

@@ -53,4 +53,22 @@ class ContextTests(TestCase):
     def test_context_comparable(self):
         test_data = {'x': 'y', 'v': 'z', 'd': {'o': object, 'a': 'b'}}
 
-        self.assertEquals(Context(test_data), Context(test_data))
+        self.assertEqual(Context(test_data), Context(test_data))
+
+        # Regression test for #21765
+        a = Context()
+        b = Context()
+        self.assertEqual(a, b)
+
+        # update only a
+        a.update({'a': 1})
+        self.assertNotEqual(a, b)
+
+        # update both to check regression
+        a.update({'c': 3})
+        b.update({'c': 3})
+        self.assertNotEqual(a, b)
+
+        # make contexts equals again
+        b.update({'a': 1})
+        self.assertEqual(a, b)