def include(arg, namespace=None):
    app_name = None
    if isinstance(arg, tuple):
        # Callable returning a namespace hint.
注释 # Callable returning a namespace hint 的意思是：下面的代码定义了一个“可调用对象”（比如函数、lambda 表达式或可调用的类），这个对象会返回一个“命名空间提示”。
        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)

假设 urlconf_module是”apps.api.urls“

再假设apps.api.urls中有app_name和url_parttens两个值

urlconf_module = import_module(urlconf_module) #相当于import apps.api import urls,而urlconf_module即是urls

也就可以

urlconf_module.app_name 等同于getattr(urlconf_module,’app_name’)

urlconf_module.url_parttens等同于getattr(urlconf_module,’url_parttens’)

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