def joint_feature(self, x, y):
        if y not in [-1, 1]:
            raise ValueError("y has to be either -1 or +1, got %s" % repr(y))
        return y * x / 2.
Set 'entry' to a sample hashed entry for twistedmatrix.com with
dataset/ETHPy150Open pystruct/pystruct/pystruct/models/unstructured_svm.py/BinaryClf.joint_feature--crossover with--dataset/ETHPy150Open kuri65536/python-for-android/python-modules/twisted/twisted/conch/test/test_knownhosts.py/HashedEntryTests.setUp