I have tried the method of installing yum on centos7. It is easy to install. I deleted it to update python2.7 before. This method is used to install it. This is the fastest and most effective installation method I found: Other Links are not good enough.
Original download address of yum package: http://mirrors.163.com/centos/7/os/x86_64/Packages/
Step 1: Download the original package. When downloading, download it according to the latest package. The downloaded package is the same as the four packages with similar names.
yum-plugin-fastestmirror*
yum-metadata-parser-*
yum-***********.centos.****.noarch.rpm
python-iniparse-****el7.noarch.rpm
Step 2: First install python
rpm -ivh python-iniparse-**************.rpm
Step 3: install the other three packages
rpm -ivh --force yum-***********.centos.**.noarch.rpm yum-metadata-parser- yum-plugin-fastestmirror
Choose to install this way.