之前的路由分发书写：

djangoProject/urls.py

from django.urls import include, re_path


urlpatterns = [
    re_path(r'^web/', include(("app01.urls", "app01"))),
]

app01/urls.py

from django.urls import re_path
from app01 import views


urlpatterns = [
    re_path(r'^index/$', views.index),
    re_path(r'^home/$', views.home),
]

app01/views.py

from django.shortcuts import render, HttpResponse

# Create your views here.


def index(request):
    return HttpResponse("index")


def home(request):
    return HttpResponse("home")

查看include源码

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)


# 返回值是一个有三个元素的元组，urlconf_module会等于'app01.urls'，urlconf_module = import_module(urlconf_module)相当于urlconf_module会等于from app01 import urls，也就是说urlconf_module会等于一个文件对象，即urls

路由分发第二种写法

from django.urls import re_path
from app01 import urls


urlpatterns = [
    path('admin/', admin.site.urls),
    re_path(r'^web/', (urls, app_name, namespace)),
]

在路由分发include中打上断点，以debug模式启动Django，查看其调用栈

 结论：

# 如果第一个参数有urls.urlpatterns属性，那么子路由就从该属性中获取
# 如果第一个参数无urls.urlpatterns属性，那么子路由就是第一个参数

路由第三种写法

djangoProject/urls.py

from django.urls import re_path
from app01 import views


urlpatterns = [
    re_path(r'^web/', ([
        re_path(r'^index/$', views.index),
        re_path(r'^home/$', views.home),
                       ], None, None))  # 可删除app01下的urls.py文件
]

正常启动Django，前端输入路由查看是否运行正常