导入错误：无法导入名称轮询

Question

我正在尝试启动https://github.com/OpenState-SDN/spider

当我尝试启动SPIDER时：

$ cd ~/spider/src
$ sudo ryu-manager SPIDER_ctrl_WEBAPP.py

我得到了

Traceback (most recent call last):
File "/usr/local/bin/ryu-manager", line 9, in 
load_entry_point('ryu==3.29', 'console_scripts', 'ryu-manager')()
File "/usr/local/lib/python2.7/dist-packages/ryu/cmd/manager.py", line 88, in main
app_mgr.load_apps(app_lists)
File "/usr/local/lib/python2.7/dist-packages/ryu/base/app_manager.py", line 401, in load_apps
cls = self.load_app(app_cls_name)
File "/usr/local/lib/python2.7/dist-packages/ryu/base/app_manager.py", line 378, in load_app
mod = utils.import_module(name)
File "/usr/local/lib/python2.7/dist-packages/ryu/utils.py", line 91, in import_module
import(name)
File "/home/mininet/spider/src/SPIDER_ctrl_WEBAPP.py", line 25, in 
import SPIDER_ctrl
File "/home/mininet/spider/src/SPIDER_ctrl.py", line 30, in 
import SPIDER_parser
File "/home/mininet/spider/src/SPIDER_parser.py", line 33, in 
from mininet.topo import Topo
File "build/bdist.linux-x86_64/egg/mininet/topo.py", line 14, in 
File "build/bdist.linux-x86_64/egg/mininet/util.py", line 7, in 

ImportError：无法导入名称轮询

Plesae，如何应对这种情况 提前谢谢