在CentOS7下，默认安装的就是python2.7，我现在来教大家如何安装python3：
1、首先安装python3.6可能使用的依赖
# yum -y install openssl-devel bzip2-devel expat-devel gdbm-devel readline-devel zlib-devel
2、下载python源码包，地址为https://www.python.org/downloads/source/，然后通过xftp上传上去，或者直接使用wget命令，wget https://www.python.org/ftp/python/3.6.1/Python-3.6.1.tgz下载到本地
# tar -zxvf Python-3.6.1.tgz
# cd Python-3.6.1/
3、把python3.6安装到/usr/local目录下
# ./configure --prefix=/usr/local/
# make
# make altinstall
4、更改/usr/bin/python链接
# cd /usr/bin
# mv python python.backup
# ln -s /usr/local/bin/python3.6 /usr/bin/python
# ln -s /usr/local/bin/python3.6 /usr/bin/python3
# rm -rf /usr/bin/python2
# ln -s /usr/bin/python2.7 /usr/bin/python2
5、更改yum脚本的python依赖
有以下文件：
-rwxr-xr-x 1 root root 802 Jan 2 17:53 yum
-rwxr-xr-x 1 root root 9374 Jan 2 17:53 yum-builddep
-rwxr-xr-x 1 root root 8091 Jan 2 17:53 yum-config-manager
-rwxr-xr-x 1 root root 7610 Jan 2 17:53 yum-debug-dump
-rwxr-xr-x 1 root root 7904 Jan 2 17:54 yum-debug-restore
-rwxr-xr-x 1 root root 10906 Jan 2 17:54 yumdownloader
-rwxr-xr-x 1 root root 11032 Jan 2 17:54 yum-groups-manager
修改以上文件头：#!/usr/bin/python 改为 #!/usr/bin/python2
可以安装一个tree测试一下
如果出现以下报错：File “/usr/libexec/urlgrabber-ext-down”, line 28
vim /usr/libexec/urlgrabber-ext-down
将/usr/bin/python改为/usr/bin/python2即可
这样，yum安装软件的时候就不会报错了，而且默认安装的就是python3了，输入python时，就会进入python3界面，如果想进入python2，那么就输入python2好了。
