django报Specifying a namespace in include() without providing an app_name is not supported.

学习了namespace的用法之后，在url后面加上了namespace，启动服务突然抛出Specifying a namespace in include() without providing an app_name is not supported.异常，我的代码如下：

urlpatterns = [
    # path('admin/', admin.site.urls),
    # path('', include(('shenghuo.urls','shenghuo'),namespace='shenghuo')),
    url('^admin/',admin.site.urls),
    url('^$',include('shenghuo.urls',namespace='shenghuo'))
]

具体的错误为：

File &/Library/Python/3.9/lib/python/site-packages/django/urls/conf.py&, line 38, in include

raise ImproperlyConfigured(

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.

我们可以看到是conf.py抛出的异常，conf.py源码如下：

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)

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('admin/', admin.site.urls),
    # path('', include(('shenghuo.urls','shenghuo'),namespace='shenghuo')),
    url('^admin/',admin.site.urls),
    url('^$',include(('shenghuo.urls','null'),namespace='shenghuos')),
]

app_name可以随便定义，但是一定要有有值，直至问题解决。

注意：django3.0之后建议使用path的方式进行url的配置，而且工程中的settings.py默认使用path的方式了。

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