Mac OS下pip安装 pillow

sudo pip install pil
报错如下：
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/tk.h:78:11: fatal error: 'X11/Xlib.h' file not found

#      include <X11/Xlib.h>

               ^

1 error generated.

error: command 'cc' failed with exit status 1


解决：

sudo pip install pillow