Add function to return list with unique elements.

Reviewed-by: ultrotter

lib/utils.py

@@ -1002,3 +1002,12 @@ def any(seq, pred=bool):
   for elem in itertools.ifilter(pred, seq):
     return True
   return False
+
+
+def UniqueSequence(seq):
+  """Returns a list with unique elements.
+
+  Element order is preserved.
+  """
+  seen = set()
+  return [i for i in seq if i not in seen and not seen.add(i)]

test/ganeti.utils_unittest.py

@@ -608,5 +608,28 @@ class TestNewUUID(unittest.TestCase):
     self.failUnless(self._re_uuid.match(utils.NewUUID()))
 
 
+class TestUniqueSequence(unittest.TestCase):
+  """Test case for UniqueSequence"""
+
+  def _test(self, input, expected):
+    self.assertEqual(utils.UniqueSequence(input), expected)
+
+  def runTest(self):
+    # Ordered input
+    self._test([1, 2, 3], [1, 2, 3])
+    self._test([1, 1, 2, 2, 3, 3], [1, 2, 3])
+    self._test([1, 2, 2, 3], [1, 2, 3])
+    self._test([1, 2, 3, 3], [1, 2, 3])
+
+    # Unordered input
+    self._test([1, 2, 3, 1, 2, 3], [1, 2, 3])
+    self._test([1, 1, 2, 3, 3, 1, 2], [1, 2, 3])
+
+    # Strings
+    self._test(["a", "a"], ["a"])
+    self._test(["a", "b"], ["a", "b"])
+    self._test(["a", "b", "a"], ["a", "b"])
+
+
 if __name__ == '__main__':
   unittest.main()