This method imports the positive and negative training data from the
        two corpus files and creates the training data list.

def import_training_data(self,
            positive_corpus_file=os.path.join(os.path.dirname(__file__),
                "positive.txt"),
            negative_corpus_file=os.path.join(os.path.dirname(__file__),
                "negative.txt")
            ):
        """
        This method imports the positive and negative training data from the
        two corpus files and creates the training data list. 
        """

        positive_corpus = open(positive_corpus_file)
        negative_corpus = open(negative_corpus_file)

        # for line in positive_corpus: 
        #     self.training_data.append((line, True))

        # for line in negative_corpus: 
        #     self.training_data.append((line, False))

        # The following code works. Need to profile this to see if this is an
        # improvement over the code above. 
        positive_training_data = list(map(lambda x: (x, True), positive_corpus))
        negative_training_data = list(map(lambda x: (x, False), negative_corpus))
        self.training_data = positive_training_data + negative_training_data