求救:python yum的rpm模块

这是我搭建linux chroot环境中 我安装了python rpm工具正常 可是yum不行 说是No module named _rpm
"/usr/local/lib/python2.4/site-packages/rpm这个目录是有的
不知道怎么解决 一下是我在python的运行结果

bash-3.2# python
Python 2.4.3 (#8, Apr 8 2011, 18:48:34) 
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> import yum
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/local/lib/python2.4/site-packages/yum/__init__.py", line 23, in ?
  import rpm
  File "/usr/local/lib/python2.4/site-packages/rpm/__init__.py", line 7, in ?
  from _rpm import *
ImportError: No module named _rpm

期盼高手的快速解决 小弟谢了

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