如何修复Django中的ModuleNotFoundError？创建应用后服务器启动失败

问题场景 #

首次未使用startapp创建应用时，服务器可正常运行。创建应用并修改views.py和urls.py后，服务器无法启动。

报错日志 #

PS E:\CS50\files\Django\demo> python manage.py runserver
Watching for file changes with StatReloader
Exception in thread django-main-thread:
Traceback (most recent call last):
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.1264.0_x64__qbz5n2kfra8p0\Lib\threading.py", line 1038, in _bootstrap_inner
    self.run()
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.1264.0_x64__qbz5n2kfra8p0\Lib\threading.py", line 975, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\utils\autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\core\management\commands\runserver.py", line 125, in inner_run
    autoreload.raise_last_exception()
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\utils\autoreload.py", line 87, in raise_last_exception
    raise _exception[1]
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\core\management\__init__.py", line 394, in execute
    autoreload.check_errors(django.setup)()
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\utils\autoreload.py", line 64, in wrapper
    fn(*args, **kwargs)
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\apps\registry.py", line 91, in populate
    app_config = AppConfig.create(entry)
                 ^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Abdul Basit Khan\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0\LocalCache\local-packages\Python311\site-packages\django\apps\config.py", line 193, in create
    import_module(entry)
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.1264.0_x64__qbz5n2kfra8p0\Lib\importlib\__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1204, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1176, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1126, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1204, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1176, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1126, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1204, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1176, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1140, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'hellodjango'

用户修改的文件内容 #

项目根目录urls.py #

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

urlpatterns = [
    path('admin/', admin.site.urls),
    path('hello/', include("hello.urls")),
]

应用hello的urls.py #

from django.urls import path
from . import views
urlpatterns = [
    path("", views.index, name="index")
]

应用hello的views.py #

from django.http import HttpResponse
from django.shortcuts import render

# Create your views here.
def index(request):
    return HttpResponse("Hello, world")

修改后的settings.py中INSTALLED_APPS部分 #

INSTALLED_APPS = [
    'hello'
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

错误原因 #

settings.py的INSTALLED_APPS列表中，'hello'末尾缺少逗号。Python会自动将相邻的字符串字面量拼接，导致'hello'和下一行的'django.contrib.admin'被合并为'hellodjango.contrib.admin'。Django启动时尝试导入这个不存在的模块，因此抛出ModuleNotFoundError: No module named 'hellodjango'。

解决方案 #

在INSTALLED_APPS列表的'hello'末尾添加逗号，修正后的配置如下：

INSTALLED_APPS = [
    'hello',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

同时确认应用已通过python manage.py startapp hello正确创建，确保hello目录下存在__init__.py、apps.py等默认生成的文件。

内容的提问来源于stack exchange，提问作者BASITO