startapp报错ModuleNotFoundError: No module named xxxxxx

现象

想创建一个新的app，报错内容如下:

PS D:\django\proj> python manage.py startapp appa
Traceback (most recent call last):
  File "manage.py", line 21, in 
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "D:\app\anaconda\lib\site-packages\django\core\management\__init__.py", line 381, in execute_from_command_line
    utility.execute()
  File "D:\app\anaconda\lib\site-packages\django\core\management\__init__.py", line 357, in execute
    django.setup()
  File "D:\app\anaconda\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "D:\app\anaconda\lib\site-packages\django\apps\registry.py", line 91, in populate
    app_config = AppConfig.create(entry)
  File "D:\app\anaconda\lib\site-packages\django\apps\config.py", line 90, in create
    module = import_module(entry)
  File "D:\app\anaconda\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "", line 1006, in _gcd_import
  File "", line 983, in _find_and_load
  File "", line 965, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'appa'

原因分析

粗一看很难看出是啥问题，报的不是manage.py的错，就是django源文件的错，这些肯定是没问题的，之前也成功创建过app。仔细看，发现中间有一个提示：

apps.populate(settings.INSTALLED_APPS)

这里提到了settings配置文件，检查一下，果然发现了问题。

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

原来，我就打算创建appa和appb两个app，就先在INSTALLED_APPS里写进去了。

解决方案

拿掉INSTALLED_APPS配置里的appa试试看，把settings文件还原

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

再运行startapp

PS D:\python\django\proj> python manage.py startapp appa
PS D:\python\django\proj> python manage.py startapp appb
PS D:\python\django\proj>

没有报错了。