code: def language_model(self,verbose=True):
          
          # use a generator in corpus
          p2 = None
          p1 = None
          for next_letter in self.corpus.next_tamil_letter():
              # update frequency from corpus
              if p2:
                  trig = p2+p1+next_letter
                  self.letter3[trig] = 1 + self.letter3.get(trig,0)
              p2 = p1
              p1 = next_letter #update always
          return
docs: builds a Tamil bigram letter model