说明： 通常Linux系统会自带Python，不需要我们安装。这里讲述的是如果安装两个不同版本的Python。如果系统的Python版本太低，刚可以安装一个新的Python。 (Linux system will usually bring their own Python, we do not need to install. Described here is that if the installation of two different versions of Python. If the system version of Python is too low, just to install a new Python.)
