Question

所以，这是我上周要求的扩展（Why do I need to import a class within this class, instead of at the top of the file?），但经过大量调试后，我觉得这可能需要一个新问题。

我有许多模块，都有导入。我怀疑可能存在循环导入，但我无法找到它。

这是奇怪的事情：

在一个models.py文件中，我有：

from django.db import models
from django.core.exceptions import ObjectDoesNotExist
from heythere.models import Notification as HeyThere
from heythere.models import NotificationManager as HeyThereManager
from django.contrib.auth.models import User

然后是一些模型定义，包括一个方法：

def to_user(self):
    try:
        return User.objects.get(username=str(self.username))
    except ObjectDoesNotExist:
        return None

又向下一点：

from ownership.apps.Assets.models import Item

当它是这样时，我得到AttributeError: 'NoneType' object has no attribute 'objects'（指用户）。所以它设置为None，不知何故，而不是提出global name XXX is not defined。

但是，我尝试在导入后立即访问用户：

me = User.objects.get(username='xxxx')
print me

在运行runserver时正确打印，因此我知道它可以在那里访问用户，但随后给了我错误消息ImportError: cannot import name Item。如何简单地访问模型导致导入错误？（FWIW，Item确实与User有许多FK关系）

是什么给出的？

包含User.objects.get()时的回溯：

  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/utils/autoreload.py", line 93, in wrapper
    fn(*args, **kwargs)
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 101, in inner_run
    self.validate(display_num_errors=True)
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/core/management/base.py", line 310, in validate
    num_errors = get_validation_errors(s, app)
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/core/management/validation.py", line 34, in get_validation_errors
    for (app_name, error) in get_app_errors().items():
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/db/models/loading.py", line 196, in get_app_errors
    self._populate()
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/db/models/loading.py", line 78, in _populate
    self.load_app(app_name)
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/db/models/loading.py", line 99, in load_app
    models = import_module('%s.models' % app_name)
  File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/utils/importlib.py", line 40, in import_module
    __import__(name)
  File "/Users/xxxxx/code/ownership/ownership/apps/Assets/models.py", line 12, in <module>
    import permissions
  File "/Users/xxxxx/code/ownership/ownership/apps/Assets/permissions.py", line 4, in <module>
    from ownership.apps.Shared.models import Person
  File "/Users/xxxxx/code/ownership/ownership/apps/Shared/models.py", line 87, in <module>
    from ownership.apps.Assets.models import Item
ImportError: cannot import name Item

没有（代码应该如何工作）：

Environment:


Request Method: POST
Request URL: http://localhost:8000/application/new

Django Version: 1.6.1
Python Version: 2.7.2
Installed Applications:
('suit',
 'south',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.redirects',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'django.contrib.admin',
 'rest_framework',
 'ldap_sync',
 'crispy_forms',
 'ownership.apps.Catalog',
 'ownership.apps.Assets',
 'ownership.apps.Shared',
 'ownership.libs.display',
 'django_tables2',
 'haystack',
 'autocomplete_light',
 'reversion',
 'heythere',
 'polymorphic',
 'django_extensions',
 'debug_toolbar')
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.contrib.redirects.middleware.RedirectFallbackMiddleware',
 'django.middleware.transaction.TransactionMiddleware',
 'reversion.middleware.RevisionMiddleware',
 'ownership.libs.shibboleth.CustomHeaderMiddleware',
 'debug_toolbar.middleware.DebugToolbarMiddleware')


Traceback:
File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  114.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/xxxxx/code/ownership/ownership/apps/Assets/crud_views.py" in connect_create_view
  48.             return subview.as_view()(request, model_name=model_name)
File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/views/generic/base.py" in view
  69.             return self.dispatch(request, *args, **kwargs)
File "/Users/xxxxx/.virtualenvs/ownership/lib/python2.7/site-packages/django/views/generic/base.py" in dispatch
  87.         return handler(request, *args, **kwargs)
File "/Users/xxxxx/code/ownership/ownership/apps/Assets/crud_views.py" in post
  280.                 create_new_asset_notification(request, new_item)
File "/Users/xxxxx/code/ownership/ownership/apps/Shared/views.py" in create_new_asset_notification
  123.                 send_email(request, subject, body, owner.to_user().email, )
File "/Users/xxxxx/code/ownership/ownership/apps/Shared/models.py" in to_user
  52.             return User.objects.get(username=str(self.username))

Exception Type: AttributeError at /application/new
Exception Value: 'NoneType' object has no attribute 'objects'

Answer 1

请注意我的堆栈跟踪：

 File "/Users/xxxxx/code/ownership/ownership/apps/Assets/models.py", line 12, in <module>
    import permissions   File "/Users/xxxxx/code/ownership/ownership/apps/Assets/permissions.py", line 4, in <module>
    from ownership.apps.Shared.models import Person   File "/Users/xxxxx/code/ownership/ownership/apps/Shared/models.py", line 87, in <module>
    from ownership.apps.Assets.models import Item

Assets/models.py正在导入permissions
Permissions正在导入Shared.models.Person
Shared/models正在导入Assets.models.Item

这是一个循环导入。

通过将from django.contrib.auth.models import User移动到Person模型内部来纠正此问题。我不太明白为什么 - 如果有人想在我接受我自己的答案之前详细说明并提供更好的解释，请做。

检测和纠正循环进口

1 个答案: