我使用Django和Python 3.7，我使用PyCharm创建了一个项目，它创建了以下目录结构（一些自定义添加是我自己的）：

mainpage
    __init__.py
    __pycache__
    admin.py
    apps.py
    fixtures
    management
    migrations
    models.py
    services.py
    templates
        mainpage
            trending.html
    tests.py
    urls.py
    views.py
mainpage_project
    __init__.py
    __pycache__
    settings
    wsgi.py
manage.py
templates
venv

文件"www.example.com"如下所示urls.py" looks like the below

from django.contrib import admin
from django.urls import path

from . import views

urlpatterns = [
    path('trending', trending, name='trending'),
]

我不知道"www.example.com"应该放在哪里，应该包含什么内容。当我启动服务器时，出现以下错误urls.py" should go and what it should contain. When I start up my server, it gives me the following error
模块未找到错误：没有名为"mainpage_project. urls"的模块

(venv) localhost:mainpage_project davea$ python manage.py runserver
Performing system checks...

Unhandled exception in thread started by <function check_errors.<locals>.wrapper at 0x103096950>
Traceback (most recent call last):
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/utils/autoreload.py", line 225, in wrapper
    fn(*args, **kwargs)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 117, in inner_run
    self.check(display_num_errors=True)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 379, in check
    include_deployment_checks=include_deployment_checks,
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/core/management/base.py", line 366, in _run_checks
    return checks.run_checks(**kwargs)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/core/checks/registry.py", line 71, in run_checks
    new_errors = check(app_configs=app_configs)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/core/checks/urls.py", line 40, in check_url_namespaces_unique
    all_namespaces = _load_all_namespaces(resolver)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/core/checks/urls.py", line 57, in _load_all_namespaces
    url_patterns = getattr(resolver, 'url_patterns', [])
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/utils/functional.py", line 37, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/urls/resolvers.py", line 533, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/utils/functional.py", line 37, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/Users/davea/Documents/workspace/mainpage_project/venv/lib/python3.7/site-packages/django/urls/resolvers.py", line 526, in urlconf_module
    return import_module(self.urlconf_name)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 965, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'mainpage_project.urls'

我的"www.example.com"文件应该放在哪里？它应该包含什么内容？urls.py" file go and what should it contain?