he following error occurred while trying to add or remove files in the
installation directory:

[Errno 13] Permission denied: '/Library/Python/2.7/site-packages/test-easy-install-2452.write-test'

The installation directory you specified (via --install-dir, --prefix, or
the distutils default setting) was:

/Library/Python/2.7/site-packages/

Perhaps your account does not have write access to this directory?  If the
installation directory is a system-owned directory, you may need to sign in
as the administrator or "root" account.  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 PYTHONPATH environment
variable.

请尝试将目标目录设置为解锁显示状态 （LION下默认隐藏）

如果还不行请sudo -s