安装编译相关工具
 

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
yum install libffi-devel -y

下载python安装包

wget http://npm.taobao.org/mirrors/python/3.9.9/Python-3.9.9.tgz
tar -zxvf  Python-3.9.9.tgz

编译安装python
mkdir /usr/local/python3 #创建编译安装目录

cd Python-3.9.9
./configure --prefix=/usr/local/python3
make && make install

安装过，出现下面两行就成功了

Installing collected packages: setuptools, pip
Successfully installed pip-21.2.4 setuptools-58.1.0

创建软连接
# 查看当前python软连接

 /usr/bin/ |grep python
lrwxrwxrwx    1 root root           7 Nov 26  2018 python -> python2
lrwxrwxrwx    1 root root           9 Nov 26  2018 python2 -> python2.7
-rwxr-xr-x      1 root root        7216 Jul 13  2018 python2.7

默认系统安装的是python2.7
删除python软连接

rm -rf /usr/bin/python

配置软连接为python3

#添加python3的软链接 

ln -s /usr/local/python3/bin/python3 /usr/bin/python

python -V

Python 3.9.9

删除默认pip软连接，并添加pip3新的软连接

rm -rf /usr/bin/pip
#添加 pip3 的软链接 

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

更改yum配置
因为其要用到python2才能执行，否则会导致yum不能正常使用（不管安装 python3的那个版本，都必须要做的）

vi /usr/bin/yum 
把 #! /usr/bin/python 修改为 #! /usr/bin/python2 
vi /usr/libexec/urlgrabber-ext-down 
把 #! /usr/bin/python 修改为 #! /usr/bin/python2
vi /usr/bin/yum-config-manager
#!/usr/bin/python 改为 #!/usr/bin/python2