docs: def compare(s1, s2, seg=True, ignore=False, stopwords=False):
      '''
      compare similarity
      s1 : sentence1
      s2 : sentence2
      seg : True : The original sentences need jieba.cut
            Flase : The original sentences have been cut.
      ignore: True: ignore OOV words
              False: get vector randomly for OOV words
      '''
      if s1 == s2: return 1.0
      
      s1_words = []
      s2_words = []
  
      if seg:
          s1 = [x for x in jieba.cut(s1, cut_all=False, HMM=False)]
          s2 = [x for x in jieba.cut(s2, cut_all=False, HMM=False)]
      else:
          s1 = s1.split()
          s2 = s2.split()
  
      # check stopwords
      if not stopwords:
          global _stopwords
          for x in s1: 
              if not x in _stopwords:
                  s1_words.append(x)
          for x in s2:
              if not x in _stopwords:
                  s2_words.append(x)
      else:
          s1_words = s1 
          s2_words = s2
  
      assert len(s1) > 0 and len(s2) > 0, "The length of s1 and s2 should > 0."
      return _similarity_distance(s1_words, s2_words, ignore)