Django之2.0版本的URL的include方法的使用

01-错误分析

在使用Django2.0，配置全局URL时，希望指向某个APP的URL，配置如下：

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

urlpatterns = [
    path('admin/', admin.site.urls),
　　# 配置users应用的URL
    path('users/', include('users.urls', namespace='users')),
]

运行该项目，会出现报错：

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.

而使用Django1.0，则会可以正常运行。

02-源码分析

在Django1.0中include的源码是：

def include(arg, namespace=None, app_name=None):
    if app_name and not namespace:
        raise ValueError('Must specify a namespace if specifying app_name.')
    if app_name:
        warnings.warn(
            'The app_name argument to django.conf.urls.include() is deprecated. '
            'Set the app_name in the included URLconf instead.',
            RemovedInDjango20Warning, stacklevel=2
        )

    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'
                )
            warnings.warn(
                'Passing a 3-tuple to django.conf.urls.include() is deprecated. '
                'Pass a 2-tuple containing the list of patterns and app_name, '
                'and provide the namespace argument to include() instead.',
                RemovedInDjango20Warning, stacklevel=2
            )
            urlconf_module, app_name, namespace = arg
    else:
        # No namespace hint - use manually provided namespace
        urlconf_module = arg

    if isinstance(urlconf_module, six.string_types):
        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:
        warnings.warn(
            'Specifying a namespace in django.conf.urls.include() without '
            'providing an app_name is deprecated. Set the app_name attribute '
            'in the included module, or pass a 2-tuple containing the list of '
            'patterns and app_name instead.',
            RemovedInDjango20Warning, stacklevel=2
        )

    namespace = namespace or app_name

    # Make sure we can iterate through the patterns (without this, some
    # testcases will break).
    if isinstance(patterns, (list, tuple)):
        for url_pattern in patterns:
            # Test if the LocaleRegexURLResolver is used within the include;
            # this should throw an error since this is not allowed!
            if isinstance(url_pattern, LocaleRegexURLResolver):
                raise ImproperlyConfigured(
                    'Using i18n_patterns in an included URLconf is not allowed.')

    return (urlconf_module, app_name, namespace)

是可以接收app_name参数的，而在Django2.0中：

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)

是不能接收app_name参数的，那么如何将参数传给app_name呢；

官方文档中指明是可以传入module的，传给变量arg的，没有传给app_name，文中提示可以传入2个参数的元组给arg，源码中有：

说明第二个元组的参数会传给app_name，找到问题解决的方法。

03-解决方案

在Django2.0中，将URL配置成：

path('users/', include(('users.urls', 'users'), namespace='users')),

04-补充

URL中的include方法之前1.0在  django.conf.urls  下，而2.0在  django.urls   下，但是之前位置还可以引用，说明在2.0中以下两种方式引用都是可以的：

from django.urls import include   

from django.conf.urls import include