pip安装python packages报错：
pip._vendor.urllib3.exceptions.ReadTimeoutError: HTTPSConnectionPool(host='pypi.tuna.tsinghua.edu.cn', port=443): Read timed out.
pip --default-timeout=100 install tensorflow==2.0.0 -i https://pypi.tuna.tsinghua.edu.cn/simple
pip --default-timeout=100 install tensorflow==2.0.0 -i https://pypi.douban.com/simple