This project is about some code I wrote when I study programming with python.
 Copyright (c) 20011-11 Yiming Yang. All rights reserved.
 This program or module is free software: you can redistribute it and/or
 modify it under the terms of the GNU General Public License as published
 by the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version. It is provided for educational
 purposes and is distributed in the hope that it will be useful, but
 WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 General Public License for more details.