参考了https://blog.csdn.net/one312/article/details/81051023这篇文章以及评论，解决了我误删系统自带Python和yum的问题。

先查下自己的centos的版本：

cat /etc/redhat-release

删除现有的python

rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps ##强制删除已安装程序及其关联
whereis python |xargs rm -frv -rf ##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 ##验证删除，返回无结果

删除现有的yum

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

从http://mirrors.163.com/centos/7/os/x86_64/Packages/下相应的包

比如，我的是7.9版本，所以我从http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/下载对应的包

wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/lvm2-python-libs-2.02.187-6.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/libxml2-python-2.9.1-6.el7.5.x86_64.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages//python-libs-2.7.5-89.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-ipaddress-1.0.16-2.el7.noarch.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-backports-1.0-8.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-backports-ssl_match_hostname-3.5.0.1-1.el7.noarch.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-2.7.5-89.el7.x86_64.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-setuptools-0.9.8-7.el7.noarch.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-chardet-2.2.1-3.el7.noarch.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/rpm-python-4.11.3-45.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-utils-1.1.31-54.el7_8.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-plugin-aliases-1.1.31-54.el7_8.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-plugin-protectbase-1.1.31-54.el7_8.noarch.rpm 
wget http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm

进行安装

rpm -Uvh --replacepkgs lvm2-python-libs*.rpm
rpm -Uvh --replacepkgs libxml2-python*.rpm
rpm -Uvh --replacepkgs python*.rpm
rpm -Uvh --replacepkgs rpm-python*.rpm yum*.rpm

如果有 Failed dependencies 的报错：

error: Failed dependencies:
dbus-python(x86-64) = 1.1.1-9.el7 is needed by dbus-python-devel-1.1.1-9.el7.x86_64
pkgconfig(dbus-1) >= 1.0 is needed by dbus-python-devel-1.1.1-9.el7.x86_64

但是又确定已经下载了这个依赖包的时候，就可以在安装的命令后加–node --force，如：

rpm -Uvh --replacepkgs libxml2-python*.rpm --nodeps --force

测试python / yum是否安装成功

python
yum