安装wechat_sender 出错： Permission denied: '/Library/Python/2.7/site-packages/singledispatch.py' pip ins

安装wechat_sender 出错：

Permission denied: '/Library/Python/2.7/site-packages/singledispatch.py'

pip install wechat_sender

查百度得到： 

https://stackoverflow.com/questions/24504231/whats-causing-this-error-when-i-try-and-install-virtualenv-ioerror-errno-13

Your account does not have write access to this directory?.

1. If the installation directory is a system-owned directory, you may need to sign in as the administrator or "root" account.
   sudo pip install virtualenv
   
2. If you do not have administrative access to this machine, you may wish to choose a different installation directory, preferably one that is listed in your PYTHON_PATH environment variable.
   
3. easier way: change that dir permission:
   chmod +a 'user:YOUR_USER_NAME allow add_subdirectory,add_file,delete_child,directory_inherit' /Library/Python/2.7/site-packages
   

解决方法：sudo chmod +a 'user:YOUR_USER_NAME allow add_subdirectory,add_file,delete_child,directory_inherit' /Library/Python/2.7/site-packages

YOUR_USER_NAME 改为自己的用户名，