症状
在本地搭建了Python的环境，网速安装库很慢，下载老是出错，出现：
pip._vendor.urllib3.exceptions.ReadTimeoutError: HTTPSConnectionPool(host=’files.pythonhosted.org’, port=443): Read timed out.
解决办法
pip install lxml --default-timeout=100
在本地搭建了Python的环境，网速安装库很慢，下载老是出错，出现：
pip._vendor.urllib3.exceptions.ReadTimeoutError: HTTPSConnectionPool(host=’files.pythonhosted.org’, port=443): Read timed out.
pip install lxml --default-timeout=100
