在centos系统下yum命令出错，可能我们就要重新安装，当python的版本升级或安装了多个python版本时，就会导致No module named yum错误。一般的解决方法都是全部删除python和yum，然后进行重装。安装过程有可能会出现python(abi) is needed等问题。
下载需要的资源：
安装包下载：http://www.rpmfind.net/
网易yum资源安装包：http://mirrors.163.com/centos/7/atomic/x86_64/Packages/
centos资源安装包：http://mirrors.aliyun.com/centos/
python资源安装包：https://centos.pkgs.org/
根据自己要系统和要求进行下载
使用的环境
Centos7.4
Python2.7.5
第一步：卸载python和卸载yum
卸载python 方法一：
rpm -qa|grep python|xargs rpm -e --allmatches --nodeps
whereis python|xargs rm -fr
卸载python 方法二：
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 ##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
卸载yum 方法一:
rpm -qa|grep yum|xargs rpm -e --allmatches --nodeps
whereis yum|xargs rm -fr
卸载yum 方法二：
rpm -qa|grep yum|sudo xargs rpm -ev –allmatches –nodeps
whereis yum |sudo xargs rm -frv
第二步下载安装包：
下载Python相关库和依赖关系安装包：
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-python-4.11.3-40.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-9.el7.noarch.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/dbus-python-devel-1.1.1-9.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-libs-2.7.5-86.el7.x86_64.rpm
wget http://mirror.centos.org/centos/7/os/x86_64/Packages/python-2.7.5-86.el7.x86_64.rpm
下载yum安装包：
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-52.el7.noarch.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-163.el7.centos.noarch.rpm
首要执行： rpm -ivh python-* rpm-python-*
没有安装错误进行yum安装
执行：rpm -ivh yum-*
如果不行进行配置Python，再进行安装
下载Python安装包：
wget https://www.python.org/ftp/python/2.7.5/Python-2.7.5.tgz
编译：
tar zxvf Python-2.7.5.tgz
cd Python-2.7.5
./configure
make && make install
然后做下软连接
ln -sf /usr/local/bin/python /usr/bin/python
查看python版本 Python -V
最后输入命令检测yum是否安装成功
没有错误安装完成
查阅问题处理
##问题一
error: Failed dependencies:
rpm = 4.11.3-40.el7 is needed by rpm-libs-4.11.3-40.el7.x86_64
##修复处理-下载包
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-4.11.3-40.el7.x86_64.rpm
##无视重新安装
rpm -Uvh rpm-4.11.3-40.el7.x86_64.rpm --nodeps --force
############################
##问题二
required to run yum. The error leading to this problem was:
/usr/lib64/python2.7/site-packages/rpm/_rpm.so: undefined symbol: rpmtsAddReinstallElement
##修复处理-下载包
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-sign-4.11.3-40.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-libs-4.11.3-40.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-build-libs-4.11.3-40.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-build-4.11.3-40.el7.x86_64.rpm
wget http://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-4.11.3-40.el7.x86_64.rpm
##无视重新安装
rpm -Uvh --replacepkgs *.rpm --nodeps --force
别的方法：
https://www.cnblogs.com/xdjun/p/11770418.html
