def update(self, new_data, *args, **kwargs):
        self.train_set += new_data
        self.train_features = [(self.extract_features(d), c)
                                for d, c in self.train_set]
        try:
            self.classifier = self.nltk_class.train(self.train_features,
                                                    *args, **kwargs)
        except AttributeError:  # Descendant has not defined nltk_class
            raise ValueError("NLTKClassifier must have a nltk_class"
                            " variable that is not None.")
        return True
Update the classifier with new training data and re-trains the
dataset/ETHPy150Open sloria/TextBlob/textblob/classifiers.py/NLTKClassifier.update