初学Python Django框架：$ python first.py runserver：报错：

Unhandled exception in thread started by
Traceback (most recent call last):
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/utils/autoreload.py", line 228, in wrapper
    fn(*args, **kwargs)
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 124, in inner_run
    self.check(display_num_errors=True)
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/core/management/base.py", line 359, in check
    include_deployment_checks=include_deployment_checks,
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/core/management/base.py", line 346, in _run_checks
    return checks.run_checks(**kwargs)
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/core/checks/registry.py", line 81, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/core/checks/urls.py", line 16, in check_url_config
    return check_resolver(resolver)
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/core/checks/urls.py", line 26, in check_resolver
    return check_method()
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/urls/resolvers.py", line 256, in check
    for pattern in self.url_patterns:
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/utils/functional.py", line 35, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/home/toohoo/.local/lib/python2.7/site-packages/django/urls/resolvers.py", line 416, in url_patterns
    raise ImproperlyConfigured(msg.format(name=self.urlconf_name))
django.core.exceptions.ImproperlyConfigured: The included URLconf '__main__' does not appear to have any patterns in it. If you see valid patterns in the file then the issue is probably caused by a circular import.
Performing system checks...

解决方法：URL映射出错，在后面加上逗号(,)，服务器跑起来了。基础待加强。。。

urlpatterns = (
    url(r'^$',index),
)

源文件first.py如下：

import os
import sys
from django.conf import settings

DEBUG = os.environ.get('DEBUG','on') == 'on'  

SECRET_KEY = os.environ.get('SECRET_KEY',os.urandom(32))
ALLOWED_HOSTS = os.environ.get('ALLOWED_HOSTS','localhost').split(',')

settings.configure(
    DEBUG = DEBUG,
    SECRET_KEY = SECRET_KEY,
    ALLOWED_HOSTS = ALLOWED_HOSTS,
    ROOT_URLCONF = __name__    
)

from django.conf.urls import url
from django.http import HttpResponse

def index(request):
    return HttpResponse('Hello World')

urlpatterns = (
    url(r'^$',index),
)

if __name__ == '__main__':
    from django.core.management import execute_from_command_line
    execute_from_command_line(sys.argv)