Fix buglet. If the input was an iterator, the fallback would occur after

part of the iterator had been consumed.   Also, fix argument names which
did not match the docs and were a bit misleading.

Lib/unittest/case.py

@@ -1003,27 +1003,26 @@ class TestCase(object):
             self.fail(self._formatMessage(msg, standardMsg))
 
 
-    def assertCountEqual(self, actual_seq, expected_seq, msg=None):
+    def assertCountEqual(self, actual, expected, msg=None):
         """An unordered sequence specific comparison. It asserts that
         actual_seq and expected_seq have the same element counts.
         Equivalent to::
 
-            self.assertEqual(Counter(iter(actual_seq)),
-                             Counter(iter(expected_seq)))
+            self.assertEqual(Counter(actual_seq),
+                             Counter(expected_seq))
 
         Asserts that each element has the same count in both sequences.
         Example:
             - [0, 1, 1] and [1, 0, 1] compare equal.
             - [0, 0, 1] and [0, 1] compare unequal.
         """
+        actual_seq, expected_seq = list(actual), list(expected)
         try:
-            actual = collections.Counter(iter(actual_seq))
-            expected = collections.Counter(iter(expected_seq))
+            actual = collections.Counter(actual_seq)
+            expected = collections.Counter(expected_seq)
         except TypeError:
             # Unsortable items (example: set(), complex(), ...)
-            actual = list(actual_seq)
-            expected = list(expected_seq)
-            missing, unexpected = unorderable_list_difference(expected, actual)
+            missing, unexpected = unorderable_list_difference(expected_seq, actual_seq)
         else:
             if actual == expected:
                 return