创建页面编辑模版之后，运行服务器。就会出现LookupError的问题

Question

问题遇到的现象和发生背景

在我创建页面编辑模版之后，运行服务器。就会出现LookupError的问题，是咋回事，是我中途编辑出现与书本内容不一致导致错误了么。我在网上看攻略是Django版本问题会出现bug，但之前都没有出现这样的问题。

问题相关代码，请勿粘贴截图

(ii_env) c:\learning_log>python manage.py runserver
Watching for file changes with StatReloader
Exception in thread Thread-1:
Traceback (most recent call last):
  File "C:\Users\a\AppData\Local\Programs\Python\Python39\lib\threading.py", line 973, in _bootstrap_inner
    self.run()
  File "C:\Users\a\AppData\Local\Programs\Python\Python39\lib\threading.py", line 910, in run
    self._target(*self._args, **self._kwargs)
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\commands\runserver.py", line 109, in inner_run
    autoreload.raise_last_exception()
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\autoreload.py", line 77, in raise_last_exception
    raise _exception[0](_exception[1]).with_traceback(_exception[2])
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\autoreload.py", line 54, in wrapper
    fn(*args, **kwargs)
  File "c:\learning_log\ii_env\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "c:\learning_log\ii_env\lib\site-packages\django\apps\registry.py", line 114, in populate
    app_config.import_models()
  File "c:\learning_log\ii_env\lib\site-packages\django\apps\config.py", line 211, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Users\a\AppData\Local\Programs\Python\Python39\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 846, in exec_module
  File "<frozen importlib._bootstrap_external>", line 983, in get_code
  File "<frozen importlib._bootstrap_external>", line 913, in source_to_code
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
SyntaxError: invalid syntax (models.py, line 26)
Traceback (most recent call last):
  File "c:\learning_log\ii_env\lib\site-packages\django\apps\registry.py", line 155, in get_app_config
    return self.app_configs[app_label]
KeyError: 'admin'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\learning_log\manage.py", line 21, in <module>
    main()
  File "c:\learning_log\manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\__init__.py", line 375, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\base.py", line 323, in run_from_argv
    self.execute(*args, **cmd_options)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\commands\runserver.py", line 60, in execute
    super().execute(*args, **options)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\base.py", line 364, in execute
    output = self.handle(*args, **options)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\commands\runserver.py", line 95, in handle
    self.run(**options)
  File "c:\learning_log\ii_env\lib\site-packages\django\core\management\commands\runserver.py", line 102, in run
    autoreload.run_with_reloader(self.inner_run, **options)
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\autoreload.py", line 579, in run_with_reloader
    start_django(reloader, main_func, *args, **kwargs)
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\autoreload.py", line 564, in start_django
    reloader.run(django_main_thread)
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\autoreload.py", line 272, in run
    get_resolver().urlconf_module
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\functional.py", line 80, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "c:\learning_log\ii_env\lib\site-packages\django\urls\resolvers.py", line 564, in urlconf_module
    return import_module(self.urlconf_name)
  File "C:\Users\a\AppData\Local\Programs\Python\Python39\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "c:\learning_log\learning_log\urls.py", line 20, in <module>
    path('admin/', admin.site.urls),  # 定义了可在管理网站中请求的所有URL
  File "c:\learning_log\ii_env\lib\site-packages\django\utils\functional.py", line 256, in inner
    self._setup()
  File "c:\learning_log\ii_env\lib\site-packages\django\contrib\admin\sites.py", line 529, in _setup
    AdminSiteClass = import_string(apps.get_app_config('admin').default_site)
  File "c:\learning_log\ii_env\lib\site-packages\django\apps\registry.py", line 162, in get_app_config
    raise LookupError(message)
LookupError: No installed app with label 'admin'.

运行结果及报错内容

LookupError: No installed app with label 'admin'.

我的解答思路和尝试过的方法

在创建页面编辑模版之前的操作，也都有运行服务器，没有出现问题。是中途编辑与书本内容不一定么，还是这步就会出现Django版本bug。

我想要达到的结果

了解问题原因，得到解决措施。

Answer 1

你新建的 app有没有放到settings.py里面？