原因

记：执行安装某个程序时将云服务器Python默认版本替换导致yum无法使用问题，并且是最坏的情况，把Python 和 yum 都删了，下面是参考的文献和解决方案
参考文献：

• YUM报错No module named yum处理
• 【故障】6、yum不可用
• No module named yum with python2.7 in centos 7

1、yum命令不能使用

There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:

   No module named yum

Please install a package which provides this module, or
verify that the module is installed correctly.

It's possible that the above module doesn't match the
current version of Python, which is:
2.7.5 (default, Oct 14 2020, 14:45:30) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)]

If you cannot solve this problem yourself, please go to 
the yum faq at:
  http://yum.baseurl.org/wiki/Faq

2、将原有Python和yum全部删除

2.1 删除Python

#删除现有的python
[root@test ~]# rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps ##强制删除已安装程序及其关联
[root@test ~]# 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
[root@test ~]# whereis python ##验证删除，返回无结果

2.2 删除yum

#删除现有的yum
[root@test ~]# rpm -qa|grep yum|xargs rpm -ev --allmatches --nodeps
[root@test ~]# whereis yum |xargs rm -frv

2.3 从阿里云镜像下载相对应的包

根据自己的系统版本去找对应Packages
如果不知道自己的系统版本，命令行输入这个cat /etc/redhat-release
阿里云镜像 developer.aliyun.com/mirror/?spm=a...
我这边使用的是CentOS7所以找对应的7版本就可以了

• 阿里云：mirrors.aliyun.com/centos/7/os/x86...

2.4 下载Python依赖的rpm包

下面是所有需要使用到的包：
需要用到的包

python-2.7.5-89.el7.x86_64.rpm
python-devel-2.7.5-89.el7.x86_64.rpm
python-iniparse-0.4-9.el7.noarch.rpm
python-kitchen-1.1.1-5.el7.noarch.rpm
python-libs-2.7.5-89.el7.x86_64.rpm
python-pycurl-7.19.0-19.el7.x86_64.rpm
python-setuptools-0.9.8-7.el7.noarch.rpm
python-urlgrabber-3.10-10.el7.noarch.rpm
rpm-python-4.11.3-45.el7.x86_64.rpm

将所有需要下载的链接放到一个txt文件中进行批量下载

https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-libs-2.7.5-89.el7.x86_64.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-2.7.5-89.el7.x86_64.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-python-4.11.3-45.el7.x86_64.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-devel-2.7.5-89.el7.x86_64.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-setuptools-0.9.8-7.el7.noarch.rpm

执行下载，并强制安装

[root@test ~]# wget -i python-rpm.txt
[root@test ~]# rpm -Uvh python-libs-2.7.5-89.el7.x86_64.rpm --nodeps
[root@test ~]# rpm -Uvh python-2.7.5-89.el7.x86_64.rpm --nodeps
[root@test ~]# rpm -Uvh python-iniparse-0.4-9.el7.noarch.rpm --nodeps
[root@test ~]# rpm -Uvh python-pycurl-7.19.0-19.el7.x86_64rpm --nodeps
[root@test ~]# rpm -Uvh python-urlgrabber-3.10-10.el7.noarch.rpm --nodepsls
[root@test ~]# rpm -Uvh rpm-python-4.11.3-45.el7.x86_64.rpm --nodeps
[root@test ~]# rpm -Uvh python-devel-2.7.5-89.el7.x86_64.rpm --nodeps
[root@test ~]# rpm -Uvh python-kitchen-1.1.1-5.el7.noarch.rpm --nodeps
[root@test ~]# rpm -Uvh python-setuptools-0.9.8-7.el7.noarch.rpm --nodeps

2.5 下载yum依赖的rpm包

https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-aliases-1.1.31-54.el7_8.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-protectbase-1.1.31-54.el7_8.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-updateonboot-1.1.31-54.el7_8.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-54.el7_8.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm

[root@test ~]# mkdir -p yum-rpm/
[root@test ~]# cd  yum-rpm/
[root@test ~]# wget -i yum-rpm.txt
[root@test ~]#  rpm -Uvh *.rpm --nodeps

3、链接新的Python命令

[root@test ~]# ln -fs /usr/bin/python2 /usr/bin/python

4、测试yum

[root@test ~]# yum

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