def pad_sentences(sentences,padding_word="<PAD/>"):
    """
    填充句子，使所有句子句子长度等于最大句子长度
    :param sentences: 
    :param padding_word: 
    :return: padded_sentences
    """
    sequence_length=max(len(x) for x in sentences)
    padded_sentences=[]
    for i in range(len(sentences)):
        sentence=sentences[i]
        num_padding=sequence_length-len(sentence)
        new_sentence=sentence+num_padding*[padding_word]
        padded_sentences.append(new_sentence)
    return padded_sentences