code: def collect_keyword (sent, ranks, stopwords):
      
      for w in sent:
          if (w.word_id > 0) and (w.root in ranks) and (w.pos[0] in "NV") and (w.root not in stopwords):
              rl = RankedLexeme(text=w.raw.lower(), rank=ranks[w.root]/2.0, ids=[w.word_id], pos=w.pos.lower(), count=1)
  
              if DEBUG:
                  print(rl)
  
              yield rl
docs: iterator for collecting the single-word keyphrases