code: def train(self): 
          
          if not self.training_data: 
              self.import_training_data()
          training_feature_set = [(self.extract_features(line), label) 
                                      for (line, label) in self.training_data]
          self.classifier = nltk.NaiveBayesClassifier.train(training_feature_set)
docs: This method generates the classifier. This method assumes that the
          training data has been loaded