Django命名组不匹配

这些是我的文件:

urls.py:

from django.conf.urls import patterns, include, url
from eiris_wipro.views import *   

urlpatterns = patterns('',
                   (r'^hello/$',hello),
                   (r'^articles/(?P)/$', restusers),
)

views.py: 来自django.http导入HttpResponse

def hello(request):
    return HttpResponse("Hello new world!")

def restusers(request, collection='smthn'):
    print 'Collection', collection
    return HttpResponse(collection)

当我尝试击球时http://127.0.0.1:8000/articles/smthn/,我收到404错误!!

我应该遗漏一些非常基本的东西.可能是什么？