django 2.0 中URL的include方法使用分析

一、问题出现：

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 url,include


urlpatterns = [
    url(r'^admin/', admin.site.urls),
　　# 配置users应用的URL
    url(r'^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。

二、原因分析：

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
        )

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

是不能接收app_name参数的，那么如何将参数传给app_name呢；

既然2.0是1.0的升级版，肯定有方法解决这个问题，查看官方文档中对include的介绍：

..........

include() also accepts as an argument either an iterable that returns URL patterns or a 2-tuple containing such iterable plus the names of the application namespaces.

Parameters:	module – URLconf module (or module name) namespace (str) – Instance namespace for the URL entries being included pattern_list – Iterable of `path()` and/or `re_path()` instances. app_namespace (str) – Application namespace for the URL entries being included

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：

if isinstance(arg, tuple):
        # Callable returning a namespace hint.
        try:
            urlconf_module, app_name = arg

说明第二个元组的参数会传给app_name，找到问题解决的方法。

三、解决方案

解决问题将URL配置换成：

url(r'^users/', include(('users.urls', 'users'), namespace='users')),

可正常启动。

四、补充

在官方文档中提示：

Changed in Django 2.0:

In older versions, this function is located in django.conf.urls. The old location still works for backwards compatibility.

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

django 2.0 中URL的include方法使用分析

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