yum不能執行 - Linux

我打上指令yum後，出現以下訊息：

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:
2.6.5 (r265:79063, Jun 30 2010, 15:40:15)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-46)]

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

不是很清楚發生了什麼問題，有人知道怎麼解決嗎？
謝謝！

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