centos7已经自带了Python2.7环境，但是不能卸载了，因为系统很多命令用的这个环境
，通过which python可以知道安装的位置

[root@master Python-3.6.2]# python
Python 2.7.5 (default, Nov  6 2016, 00:28:07) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()
[root@master Python-3.6.2]# which python
/usr/bin/python

安装Python3环境

执行下面两个命令：

# 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 libffi-devel

在线下载安装包：
本人用的是3.6.2版，其他版自己在官网找到链接，然后通过wget下载
官网地址：https://www.python.org/downloads/source/

wget https://www.python.org/ftp/python/3.6.2/Python-3.6.2.tar.xz

创建一个Python3的文件夹

# mkdir /usr/local/python3

解压刚刚下载的文件，进入解压后的文件夹，再继续操作

# tar -xvJf Python-3.6.2.tar.xz 
# cd Python-3.6.2
# ./configure --prefix=/usr/local/python3
# make
# make install

如果make命令没有安装的可以执行下面安装一下,在执行上面步骤

#yum install make
#yum install cmake
#yum install cmake

make install命令执行完后，/usr/local/python3会有文件，最后创建软链接

# ln -s /usr/local/python3/bin/python3 /usr/bin/python3
# ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3

最后输入python3测试是否已安装成功

[root@master Python-3.6.2]# python3
Python 3.6.2 (default, Jun 27 2018, 17:07:22) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-28)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()
[root@master Python-3.6.2]#