Mac OS 下virtualenv的安装与使用

安装

我使用以下命令安装virtualenv是出现的问题：

sudo pip install virtualevn

The directory '/Users/Carrie/Library/Caches/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/Users/Carrie/Library/Caches/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
Collecting virtualevn
  Could not find a version that satisfies the requirement virtualevn (from versions: )
No matching distribution found for virtualevn

然后换成以下命令就能成功安装了：

sudo pip --trusted-host pypi.python.org install virtualenv
The directory '/Users/Carrie/Library/Caches/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/Users/Carrie/Library/Caches/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
Collecting virtualenv
  Downloading virtualenv-15.1.0-py2.py3-none-any.whl (1.8MB)
    100% |████████████████████████████████| 1.8MB 134kB/s 
Installing collected packages: virtualenv
Successfully installed virtualenv-15.1.0