我正在学习Django使用书“轻量级Django”。我正在使用Django 1.8。但是，我不能运行此代码。以下是错误消息：

工作树：

build.py

import os
import shutil

from django.conf import settings
from django.core.management import call_command
from django.core.management.base import BaseCommand
from django.core.urlresolvers import reverse
from django.test.client import Client

def get_pages():
    for name in os.listdir(settings.SITE_PAGES_DIRECTORY):
        if name.endswith('.html'):
            yield name[:-5]

class Command(BaseCommand):
    help = 'Build static site output.'
    leave_locale_alone = True

    def handle(self, *args, **options):
        if os.path.exists(settings.SITE_OUTPUT_DIRECTORY):
            shutil.rmtree(settings.SITE_OUTPUT_DIRECTORY)
        os.mkdir(settings.SITE_OUTPUT_DIRECTORY)
        os.makedirs(settings.STATIC_ROOT, exists_ok=True)
        call_command('collectstatic', interactive=False, clear=True,verbosity=0)
        client = Client()
        for page in get_pages():
            url = reverse('page', kwargs={'slug': page})
            response = client.get(url)
            if page == 'index':
                output_dir = settings.SITE_OUTPUT_DIRECTORY
            else:
                output_dir = os.path.join(settings.SITE_OUTPUT_DIRECTORY, page)
                os.makedirs(output_dir)
            with open(os.path.join(output_dir, 'index.html'), 'wb') as f:
                f.write(response.content)

prototypes.py

import os
import sys
from django.conf import settings

BASE_DIR = os.path.dirname(__file__)

settings.configure(
    DEBUG = True,
    SECRET_KEY= 'qfzf!b1z^5dyk%syiokeg4*2xf%kj68g=o&e8qvd@@(1lj5z8)',
    ROOT_URLCONF='sitebuilder.urls',
    MIDDLEWARE_CLASSES=(),
    INSTALLED_APPS=(
        'django.contrib.staticfiles',
        'sitebuilder',
    ),

    TEMPLATES=(
        {
            'BACKEND':'django.template.backends.django.DjangoTemplates',
            'DIRS':[],
            'APP_DIRS':True,
        },
    ),
    STATIC_URL='/static/',
    SITE_PAGES_DIRECTORY=os.path.join(BASE_DIR,'pages'),
    SITE_OUTPUT_DIRECTORY=os.path.join(BASE_DIR,'_build'),
    STATIC_ROOT=os.path.join(BASE_DIR,'_build','static'),
)



if __name__ == "__main__":
    from django.core.management import execute_from_command_line

    execute_from_command_line(sys.argv)