code: def update(self, new_data, *args, **kwargs):
          '''Update the classifier with new training data and re-trains the
          classifier.
  
          :param new_data: New data as a list of tuples of the form
              ``(text, label)``.
          '''
          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 Truf update(self, new_data, *args, **kwargs):
          '''Update the classifier with new training data and re-trains the
          classifier.
  
          :param new_data: New data as a list of tuples of the form
              ``(text, label)``.
          '''
          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
docs: Update the classifier with new training data and re-trains the
          classifier.
  
          :param new_data: New data as a list of tuples of the form
              ``(text, label)``.