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

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)