title: Remove clearly and reinstall python on CentOS
body: <p>Today I messed up the versions of Python on my CentOS machine. Even <code>yum</code> cannot work properly. I made the mistake that I removed the default <code>/usr/bin/python</code> which led to this situation. How could I get back a clear Python environment? I thought remove them totally and reinstall Python may work, but do not know how to do it. Wish somebody could help!</p>