1、删除现有Python

#强制删除已安装程序及其关联
rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps

#强制删除已安装程序及其关联
rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps 

##删除所有残余文件 ##xargs，允许你对输出执行其他某些命令
whereis python |xargs rm -frv 

##验证删除，返回无结果
whereis python 

2、删除现有的yum

rpm -qa|grep yum|xargs rpm -ev --allmatches --nodeps
whereis yum |xargs rm -frv

3.下载

#如果下载时文件不存在 404 Not Found或者还有其他有需要的rpm包，到 http://mirrors.163.com/centos/7/os/x86_64/Packages 查找核对存在的版本

wget http://mirrors.163.com/centos/7/os/x86_64/Packages/libxml2-python-2.9.1-6.el7.5.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-build-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-build-libs-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-libs-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-sign-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-python-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-2.7.5-89.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/dbus-python-devel-1.1.1-9.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-libs-2.7.5-89.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-setuptools-0.9.8-7.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-backports-1.0-8.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-backports-ssl_match_hostname-3.5.0.1-1.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-chardet-2.2.1-3.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-ipaddress-1.0.16-2.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-virtualenv-15.1.0-4.el7_7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-54.el7_8.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-protectbase-1.1.31-54.el7_8.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-aliases-1.1.31-54.el7_8.noarch.rpm

安装

rpm -Uvh --force --nodeps --replacepkgs *.rpm