（一）简述
刚安装的centos7.4版本默认是安装Python2.7，由于一些命令需要使用的原因，比如yum等，使用的是2.7.5版本的，由于现在很多库包括django都是使用Python3,
因此，有这样的需求：yum使用python2.7版本，django和其他的使用默认的python3版本。
（二）查看并备份python2相关信息
1，使用python -V 可以查看默认的版本信息。
[root@localhost ~]# python -V
Python 2.7.52，然后使用which python 查看下python的可执行文件的位置。
[root@localhost ~]# which python
/usr/bin/python3，可执行文件在/usr/bin/目录下，查看有关python的文件，ll /usr/bin/python*。通过查看可以得知python默认指向的是python2.7
[root@localhost ~]# ll /usr/bin/python*
lrwxrwxrwx. 1 root root 7 Dec 21 15:23 /usr/bin/python -> python2
lrwxrwxrwx. 1 root root 9 Dec 21 15:23 /usr/bin/python2 -> python2.7
-rwxr-xr-x. 1 root root 7136 Aug 4 2017 /usr/bin/python2.7重要：通过查看可以得知python默认指向的是python2.7，由于还没有安装python3,可以先备份python文件，等python3安装好了后再创建软连接即可
4，备份默认python2.7版本
[root@localhost bin]# mv /usr/bin/python /usr/bin/python.bak
（三）方法一：安装配置python3
1，安装相关的包yum -y install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gcc make
[root@localhost bin]# yum install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gcc make
Loaded plugins: fastestmirror
base | 3.6 kB 00:00:00
extras | 3.4 kB 00:00:00
updates | 3.4 kB 00:00:00
Loading mirror speeds from cached hostfile
Package zlib-devel-1.2.7-17.el7.x86_64 already installed and latest version
Package 1:openssl-devel-1.0.2k-8.el7.x86_64 already installed and latest version
Package ncurses-devel-5.9-14.20130511.el7_4.x86_64 already installed and latest version
Package sqlite-devel-3.7.17-8.el7.x86_64 already installed and latest version
Package gcc-4.8.5-16.el7_4.1.x86_64 already installed and latest version
Package 1:make-3.82-23.el7.x86_64 already installed and latest version
Resolving Dependencies
--> Running transaction check
---> Package bzip2-devel.x86_64 0:1.0.6-13.el7 will be installed2，去python官网下载稳定版（https://www.python.org/ftp/python/3.6.4/Python-3.6.4.tar.xz）
[root@localhost usr]# wget https://www.python.org/ftp/python/3.6.4/Python-3.6.4.tar.xz
--2018-03-08 00:05:54-- https://www.python.org/ftp/python/3.6.4/Python-3.6.4.tar.xz
Resolving www.python.org (www.python.org)... 151.101.228.223, 2a04:4e42:12::223
Connecting to www.python.org (www.python.org)|151.101.228.223|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 16992824 (16M) [application/octet-stream]
Saving to: ‘Python-3.6.4.tar.xz’
16% [==============> ] 2,781,624 49.4KB/s eta 4m 49s3，安装python3
[root@localhost tmp]# tar xf Python-3.6.1.tar.xz
[root@localhost tmp]# cd Python-3.6.1
[root@localhost Python-3.6.1]# ./configure prefix=/usr/local/python3
[root@localhost Python-3.6.1]# make &&make install4,在/usr/bin/下创建软连接
[root@localhost Python-3.6.1]# ln -s /usr/local/python3/bin/python3 /usr/bin/python
[root@localhost Python-3.6.1]# python -V
Python 3.6.1
[root@localhost Python-3.6.1]# python2 -V
Python 2.7.5
[root@localhost Python-3.6.1]# ll /usr/bin/python*
lrwxrwxrwx 1 root root 32 Mar 7 05:38 /usr/bin/python -> /usr/local/python3.6/bin/python3
lrwxrwxrwx. 1 root root 9 Jan 29 16:34 /usr/bin/python2 -> python2.7
-rwxr-xr-x. 1 root root 7136 Aug 4 2017 /usr/bin/python2.7
lrwxrwxrwx. 1 root root 7 Jan 29 16:34 /usr/bin/python2.bak -> python25，配置正常使用yum，使yum使用python2.7版本，否则会报错的。
5.1，修改/usr/bin/yum文件把#! /usr/bin/python修改为#! /usr/bin/python2
[root@localhost Python-3.6.1]# vim /usr/bin/yum
#!/usr/bin/python25.2，修改/usr/libexec/urlgrabber-ext-down文件，把里面的#! /usr/bin/python 也要修改为#! /usr/bin/python2
[root@localhost Python-3.6.1]# vim /usr/libexec/urlgrabber-ext-down
#! /usr/bin/python26，如果使用pip的话，简历pip3的软连接。
[root@localhost Python-3.6.1]#ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3
[root@localhost Python-3.6.1]# ll /usr/bin/pip3
lrwxrwxrwx 1 root root 29 Mar 7 05:41 /usr/bin/pip3 -> /usr/local/python3.6/bin/pip3至此，一台服务器上默认的版本是python3 ,同时python2页存在了，可以正常使用yum来进行安装所需的软件了。