Fixed #18340 -- Fixed formtools form_hmac with Unicode input

Using cPickle, two apparently identical Unicode strings could
generate different pickled results depending on previous operations
on those strings.

django/contrib/formtools/tests/__init__.py

@@ -156,18 +156,15 @@ def test_form_submit_bad_hash(self):
 
 
 class FormHmacTests(unittest.TestCase):
-    """
-    Same as SecurityHashTests, but with form_hmac
-    """
 
     def test_textfield_hash(self):
         """
         Regression test for #10034: the hash generation function should ignore
         leading/trailing whitespace so as to be friendly to broken browsers that
         submit it (usually in textareas).
         """
-        f1 = HashTestForm({'name': 'joe', 'bio': 'Nothing notable.'})
-        f2 = HashTestForm({'name': '  joe', 'bio': 'Nothing notable.  '})
+        f1 = HashTestForm({'name': u'joe', 'bio': u'Nothing notable.'})
+        f2 = HashTestForm({'name': u'  joe', 'bio': u'Nothing notable.  '})
         hash1 = utils.form_hmac(f1)
         hash2 = utils.form_hmac(f2)
         self.assertEqual(hash1, hash2)

django/contrib/formtools/utils.py

@@ -1,7 +1,5 @@
-try:
-    import cPickle as pickle
-except ImportError:
-    import pickle
+# Do not try cPickle here (see #18340)
+import pickle
 
 from django.utils.crypto import salted_hmac