在机器中分别装了2个比系统默认版本高的python后，再次使用yum的时候发现报错了，如下：

[root@localhost ~]# yum
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:
2.6.8 (unknown, Jun 18 2015, 16:07:56) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-4)]

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

yum是用python实现的，应该是默认执行时用了不匹配的版本，将yum中的python版本改到能import yum模块的即可。

• 查看系统中有哪些python

  [root@localhost ~]# whereis python
  python: /usr/bin/python2.6-config /usr/bin/python /usr/bin/python2.6 /usr/lib/python2.6 /usr/lib64/python2.6 /usr/local/bin/python2.6-config /usr/local/bin/python /usr/local/bin/python2.7-config /usr/local/bin/python2.7 /usr/local/bin/python2.6 /usr/local/lib/python2.7 /usr/local/lib/python2.6 /usr/include/python2.6 /usr/share/man/man1/python.1.gz
  

• 先测试2.6的

  [root@localhost ~]# /usr/bin/python2.6
  Python 2.6.6 (r266:84292, Nov 22 2013, 12:16:22) 
  [GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import yum
  >>> exit()
  

  再测试默认2.7.10的

  [root@localhost ~]# python
  Python 2.7.10 (default, Jun 18 2015, 15:51:08) 
  [GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import yum
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  ImportError: No module named yum
  >>> exit()
  

• 修改yum的默认python版本

  [root@localhost ~]# vim /usr/bin/yum
  #!/usr/bin/python2.6