What is wrong about this openstack error
<p>I install openstack (liberty) on my server, after I installed the openstack client package, but, I meet such error when I execute openstack:</p>

<pre><code>[root@node0 tools]# openstack
Traceback (most recent call last):
File "/usr/bin/openstack", line 6, in &lt;module&gt;
from openstackclient.shell import main
File "/usr/lib/python2.7/site-packages/openstackclient/shell.py", line 24, in &lt;module&gt;
from cliff import app
File "/usr/lib/python2.7/site-packages/cliff/app.py", line 14, in &lt;module&gt;
from .complete import CompleteCommand
File "/usr/lib/python2.7/site-packages/cliff/complete.py", line 10, in &lt;module&gt;
from cliff import command
File "/usr/lib/python2.7/site-packages/cliff/command.py", line 9, in &lt;module&gt;
@six.add_metaclass(abc.ABCMeta)
AttributeError: 'module' object has no attribute 'add_metaclass'
</code></pre>

<p>what is the problem happend? My OS is centos7, what I did when I install python-openstackclient like this:</p>

<pre><code>[root@node0 tools]# yum install python-openstackclient

List item

Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
* base: mirrors.btte.net
* epel: ftp.riken.jp
* extras: mirrors.yun-idc.com
* updates: mirrors.btte.net
Resolving Dependencies
--&gt; Running transaction check
---&gt; Package python-openstackclient.noarch 0:1.7.1-1.el7 will be    installed
--&gt; Finished Dependency Resolution

Dependencies Resolved

 ============================================================================================================================================

   Package                                Arch                      Version                        Repository                                Size
    =============================================================================================================================================
   Installing:
   python-openstackclient                 noarch                 1.7.1-1.el7                    centos-openstack-liberty                 431 k

   Transaction Summary

   =============================================================================================================================================
   Install  1 Package

   Total download size: 431 k
   Installed size: 2.6 M
   Is this ok [y/d/N]: y
   Downloading packages:
   python-openstackclient-  1.7.1-1.el7.noarch.rpm                                                                         | 431 kB  00:00:05     
   Running transaction check
   Running transaction test
   Transaction test succeeded
   Running transaction
   Installing : python-openstackclient- 1.7.1-1.el7.noarch                                                                                 1/1 
   Verifying  : python-openstackclient-   1.7.1-1.el7.noarch                                                                                 1/1 

   Installed:
   python-openstackclient.noarch  0:1.7.1-1.el7                                                                                                

   Complete!
</code></pre>

<p>please help me to check what happened! any suggestion is welcomed, thanks!</p>