def calculate_term_frequencies(self):
		"""Q.calculate_term_frequencies() -- calculate the number of times 
		each term t occurs in document d.
		"""
		for doc in self.processed_corpus:
			term_frequency_doc = defaultdict(int)
			for word in doc:
				term_frequency_doc[word] += 1
			
			for key,value in term_frequency_doc.iteritems():
				term_frequency_doc[key] = (1.0 * value) / len(doc)
			self.term_frequencies.append(term_frequency_doc)
Q.calculate_term_frequencies() -- calculate the number of times 
		each term t occurs in document d.