How do you use Django URL namespaces?

I'm trying to get the hang of Django URL namespaces. But I can't find any examples or documentation.

Here is what I have tried.

urls.py:

from django.conf.urls.defaults import *urlpatterns = patterns('',    (r'^foo/', include('sub_urls', namespace='foo', app_name='foo')),    (r'^bar/', include('sub_urls', namespace='bar', app_name='bar')),            )

sub_urls.py:

from django.conf.urls.defaults import patterns, urlfrom views import view1urlpatterns = patterns('views',    url(r'^(?P<view_id>\d+)/$', view1, name='view1'))

views.py:

from django.shortcuts import render_to_responsedef view1(request, view_id):    return render_to_response('view1.html', locals())

In view1.html, {% url foo:view1 3 %} outputs /foo/3, and {% url bar:view1 3 %} outputs /bar/3. This holds true whether I browse to /foo/X or /bar/X.

What I want is to be able to browse to /foo/X or /bar/X, and have {% url view1 3 %} output either /foo/3 or /bar/3, respectively.