python升级后yum报错问题

centos默认python版本是2.6，升级到2.7后，发现yum不能用了

报错内容：

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:
2.7.10 (default, Aug 25 2017, 11:09:17)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-17)]

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

解决办法：

vi /usr/bin/yum

编辑首行，
#!/usr/bin/python

修改成
#!/usr/bin/python2.6

再次执行yum就没有问题啦