Django2.0报错：Specifying a namespace in include() without providing an app_name is not supported.

本地环境

• Python: 3.6.0
• Django: 2.0

报错信息

部分：

  File "/Users/Documents/D-develope/DjangoDemo/TestPro/TestPro/urls.py", line 22, in <module>
    path('demo1/', include('demo1.urls', namespace='demo1')),
  File "/Users/.pyenv/versions/3.6.0/lib/python3.6/site-packages/django/urls/conf.py", line 39, in include
    'Specifying a namespace in include() without providing an app_name '
django.core.exceptions.ImproperlyConfigured: Specifying a namespace in include() without providing an app_name is not supported. Set the app_name attribute in the included module, or pass a 2-tuple containing the list of patterns and app_name instead.

问题原因

• 我的代码

urlpatterns = [
    path('demo1/', include('demo1.urls', namespace='demo1'),
]

• 查看报错信息指向"django/urls/conf.py", line 39";
  源代码如下：

def include(arg, namespace=None):
    app_name = None
    if isinstance(arg, tuple):
        # Callable returning a namespace hint.
        try:
            urlconf_module, app_name = arg
        except ValueError:
            if namespace:
                raise ImproperlyConfigured(
                    'Cannot override the namespace for a dynamic module that '
                    'provides a namespace.'
                )
            raise ImproperlyConfigured(
                'Passing a %d-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.' % len(arg)
            )
    else:
        # No namespace hint - use manually provided namespace.
        urlconf_module = arg

    if isinstance(urlconf_module, str):
        urlconf_module = import_module(urlconf_module)
    patterns = getattr(urlconf_module, 'urlpatterns', urlconf_module)
    app_name = getattr(urlconf_module, 'app_name', app_name)
    if namespace and not app_name:
        raise ImproperlyConfigured(
            'Specifying a namespace in include() without providing an app_name '
            'is not supported. Set the app_name attribute in the included '
            'module, or pass a 2-tuple containing the list of patterns and '
            'app_name instead.',
        )
    namespace = namespace or app_name
    # Make sure the patterns can be iterated through (without this, some
    # testcases will break).
    if isinstance(patterns, (list, tuple)):
        for url_pattern in patterns:
            pattern = getattr(url_pattern, 'pattern', None)
            if isinstance(pattern, LocalePrefixPattern):
                raise ImproperlyConfigured(
                    'Using i18n_patterns in an included URLconf is not allowed.'
                )
    return (urlconf_module, app_name, namespace)

修改方案

从include()函数可以看出来，这个函数有两个参数，一个arg，一个namespace，我在代码中也是两个参数，但是异常中提示了，没有提供app_name，还提示需要传入一个两元元组，从第六行代码
urlconf_module, app_name = arg 可以看出来，arg就是那个元组，且给app_name赋值了，所以我们这里修改代码为：

urlpatterns = [
    path('demo1/', include(('demo1.urls', 'demo1'), namespace='demo1')),