NameError name 'lang' is not defined, corresponds to name 'polls' is not defined,

I am trying to create a project "lang" according Django documentation part 1-4 tutorial.

Folder structure:

Scripts\lang\lang\_init_.py
Scripts\lang\lang\settings.py
Scripts\lang\lang\urls.py

Scripts\lang\langu\_init_.py
Scripts\lang\langu\admin.py
Scripts\lang\langu\models.py
Scripts\lang\langu\urlsu.py
Scripts\lang\langu\views.py

************* Scripts\lang\lang\urls.py
from django.conf.urls import patterns, include, url

from django.contrib import admin
admin.autodiscover()

from langu import views

urlpatterns = patterns('',              
    url(r'^langu/', include(langu.urlsu)),                   
    url(r'^admin/', include(admin.site.urls)),
)


************* Scripts\lang\langu\urlsu.py
from django.conf.urls import patterns, url

from langu import views

urlpatterns = patterns('',
    url(r'^$', views.index, name='index')
)


************* Scripts\lang\lang\settings.py
...
INSTALLED_APPS = (
    'django.contrib.admin',
    'langu',
)
ROOT_URLCONF = 'lang.urls'
....




************* Scripts\lang\langu\views.py
from django.shortcuts import render
from django.http import HttpResponse

def index(request):
    return HttpResponse("Hello, world. You're at the poll index.")

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