Django2.1 include()函数报错'provide the namespace argument to include() instead.' % len(arg)

《Python编程：从入门到实践》项目三 Web应用程序

书中原来的程序

from django.conf.urls import include, url
from django.contrib import admin

urlpatterns = [
    url(r'^admin/', include(admin.site.urls)),
    url(r'', include('learning_logs.urls', namespace='learning_logs')),
]

在Terminal中运行：

(ll_env) F:\Python\pycharm-workspace\learning_log>python manage.py runserver

 运行报错：

File "F:\Python\pycharm-workspace\learning_log\lear
ning_log\urls.py", line 22, in <module>
    url(r'^admin/', include(admin.site.urls)),
  File "F:\Python\pycharm-workspace\learning_log\ll_e
nv\lib\site-packages\django\urls\conf.py", line 27, in include
    'provide the namespace argument to include() instead.' % len(arg)
django.core.exceptions.ImproperlyConfigured: Passing a 3-tuple to include() is not supported. Pass a 2-tuple containing the list of patterns and app_name, and provide
 the namespace argument to include() instead.

 修改：

from django.conf.urls import include, url
from django.contrib import admin

urlpatterns = [
    url(r'^admin/', admin.site.urls),# 不用include()函数
    url(r'', include(('learning_logs.urls','learning_logs'), namespace='learning_logs')),
    # url(r'', include('learning_logs.urls')), # 或者修改为include(pattern_list)这种用法也是可以的！！！
]

 报错原因如下：

 最后查找资料，Django2.1的官方文档。

根据文档的提示，admin.site.urls不用include()函数。书中第二个include()函数没有提供app_namespace，所以会报错！

修改好就可以正常运行了！