MAC下使用pip安装pil时有时会出现这种错误：
Could not find a version that satisfies the requirement PIL (from versions: )
No matching distribution found for PIL
此时可以改用在pycharm终端中使用 sudo命令来安装
ex: py2.x sudo pip install Pillow
py3.x. sudo pip3 install Pillow
或者可以使用pycharm自带的安装器来安装