Could not find an activated virtualenv (required)解决方案

Could not find an activated virtualenv (required)

在执行pip install --upgrade pip时报错

Could not find an activated virtualenv (required)解决方案
网上解决方案如下:
https://www.e-learn.cn/content/wangluowenzhang/309242

但以上解决方案都没有解决我的问题,最终我的解决方式如下,末尾加–isolated:
sudo ./pip install --upgrade pip –isolated
Could not find an activated virtualenv (required)解决方案
安装虚拟环境:
Could not find an activated virtualenv (required)解决方案