code: def tokenize(self, text, include_punc=True, nested=False):
          
          self.tokens = [
              w for w in (
                  self.word_tokenize(
                      s,
                      include_punc) for s in self.sent_tokenize(text))]
          if nested:
              return self.tokens
          else:
              return list(chain.from_iterable(self.tokens))
docs: Return a list of word tokens.
  
          :param text: string of text.
          :param include_punc: (optional) whether to include punctuation as separate
              tokens. Default to True.
          :param nested: (optional) whether to return tokens as nested lists of
              sentences. Default to False.