Fixed SortedDict.__copy__()

Fixed #18175 -- Calling SortedDict.__copy__() resulted in changes to
the original dictionary. The reason was likely related to subclassing
dict.

Thanks to linovia for report and patch.

django/utils/datastructures.py

@@ -128,6 +128,12 @@ class SortedDict(dict):
         return self.__class__([(key, copy.deepcopy(value, memo))
                                for key, value in self.iteritems()])
 
+    def __copy__(self):
+        # The Python's default copy implementation will alter the state
+        # of self. The reason for this seems complex but is likely related to
+        # subclassing dict.
+        return self.copy()
+
     def __setitem__(self, key, value):
         if key not in self:
             self.keyOrder.append(key)
@@ -200,9 +206,7 @@ class SortedDict(dict):
     def copy(self):
         """Returns a copy of this object."""
         # This way of initializing the copy means it works for subclasses, too.
-        obj = self.__class__(self)
-        obj.keyOrder = self.keyOrder[:]
-        return obj
+        return self.__class__(self)
 
     def __repr__(self):
         """

tests/regressiontests/utils/datastructures.py

@@ -111,6 +111,12 @@ class SortedDictTests(SimpleTestCase):
             {7: 'seven', 1: 'one', 9: 'nine'}
         )
 
+    def test_copy(self):
+        orig = SortedDict(((1, "one"), (0, "zero"), (2, "two")))
+        copied = copy.copy(orig)
+        self.assertEqual(orig.keys(), [1, 0, 2])
+        self.assertEqual(copied.keys(), [1, 0, 2])
+
     def test_clear(self):
         self.d1.clear()
         self.assertEqual(self.d1, {})