系统自带python2，通过annaconda3，使用python3：
1. cd Downloads/
2. wget https://repo.continuum.io/archive/Anaconda3-5.0.1-Linux-x86_64.sh
3. chmod +x Anaconda3-5.0.1-Linux-x86_64.sh
4. ./Anaconda3-5.0.1-Linux-x86_64.sh
5. vim ~/.bashrc
* append "export PATH=$PATH:$HOME/anaconda3/bin" at last ## 设置环境变量时，新安装的anaconda3的地址最好放在最后，因为centos7有些系统服务会使用到系统自带的python2
6. source ~/.bashrc
if you are the 'root':
7. do the above 1~5 steps
8. vim /etc/profile
* append "export PATH=$PATH:/root/anaconda3/bin" at last
9. source ~/.bashrc
10. cd /usr/bin
11. ln -s /root/anaconda3/bin/python3.6 python3 ## 创建一个软连接，这样调用python3时，会启动anaconda内的程序
12. chmod o+x /root
then every user can use 'python3' directly