Could not find a version that satisfies the requirement Werkzeug>=0.15 (from flask) (from versions: none)的解决

在dos命令窗口输入pip install flask 遇到错误

错误：

ERROR: Could not find a version that satisfies the requirement Werkzeug>=0.15 (from flask) (from versions: none)
ERROR: No matching distribution found for Werkzeug>=0.15 (from flask)

解决办法

　　1.  pip --trusted-host pypi.python.org install 安装包名字(flask)

　　2.  再不行 用镜像网站

　　pip install 安装包名字 -i http://pypi.doubanio.com/simple/ --trusted-host pypi.doubanio.com