注意事项：
1、非root帐号加上sudo
2、centos7自带Python 2.7.5是不能卸载的，很多系统级软件依赖这个

安装依赖
# yum -y groupinstall "Development tools"
# yum -y install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel xz-devel

下载python3，我的是Python-3.4.2.tgz
# wget https://www.python.org/ftp/python/3.4.2/Python-3.4.2.tgz
# mkdir /usr/local/python3 
# tar -zxvf Python-3.4.2.tgz
# cd Python-3.4.2
# ./configure --prefix=/usr/local/python3
# make && make install
# ln -s /usr/local/python3/bin/python3 /usr/bin/python3

测试
查看版本
# python3
Python 3.4.2 (default, Jul 19 2016, 03:47:32) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

代码测试
在当前目录新建个python脚本hello.py
内容:
#!/usr/bin/python3
# 第一个注释
print ("Hello, Python3!") 
执行
# python3 hello.py

Hello, Python3!