sudo apt-get clean
sudo rm -rf /var/lib/apt/lists/*
https://blog.csdn.net/myboyliu2007/article/details/85112421
python copy()和deepcopy()https://iaman.actor/blog/2016/04/17/copy-in-python
自然语言处理全家福：纵览当前NLP中的任务、数据、模型与论文
https://github.com/huangxiangzhou/NLPCC2016KBQA
https://github.com/ljpzzz/machinelearning/blob/master/natural-language-processing/lda.ipynb