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:
2.7.14 (default, Nov 23 2017, 00:22:39) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-55)]

If you cannot solve this problem yourself, please go to 
the yum faq at:
  http://wiki.linux.duke.edu/YumFaq

解决方案：

1、查看当前系统python版本

python -V

Python 2.7.14

2、查看python安装路径使用：whereis python

python: /usr/bin/python2.4 /usr/bin/python /usr/lib/python2.4 /usr/lib/python2.6 /usr/lib/python2.7 /usr/include/python2.4 /usr/include/python2.6 /usr/share/man/man1/python.1.gz

3、查看 ：which yum

     编辑:vi /usr/bin/yum

     如下图所示：

  /usr/bin/yum 默认为#!/usr/bin/python ，上图划线部分我已经修改为：#!/usr/bin/python2.4 保存即可