源码下载：
wget http://www.dnspython.org/kits/1.9.4/dnspython-1.9.4.tar.gz
解压缩：
tar zxvf dnspython-1.9.4.tar.gz
安装：
python setup.py install
测试：
[root@bogon dnspython-1.9.4]# python
\Python 2.6.6 (r266:84292, Jul 23 2015, 15:22:56)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-11)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
import dns
记住模块名字是 dns，可以看到我们安装成功
