python2.7.3安装libxml2，导入import lxml.html报?报错

系统是red hat ，自带的是2.6.6版本的python，但最近需要使用scrapy需要安装2.7.3版本的
,通过yum install 安装的libxml2，安装成功后import lxml没有报错，但import lxml.html
时就报错了，报错信息如下：

import lxml.html
Traceback (most recent call last):
File "", line 1, in
File "/usr/local/lib/python2.7/site-packages/lxml/html/__init__.py", line 12, in
from lxml import etree
File "lxml.etree.pyx", line 89, in init lxml.etree (src/lxml/lxml.etree.c:140164)
TypeError: encode() argument 1 must be string without null bytes, not unicode

求各位python大神指导...