在 django urls 中出现循环导入错误

Question

我在项目级urls.py文件中收到以下循环导入错误：

ImproperlyConfigured: The included URLconf 'pres_value.urls' does not appear to have any patterns in it. If you see valid patterns in the file then the issue is probably caused by a circular import.

需要明确的是，pres_value是项目级别，present是应用级别。所以显然错误发生在项目级urls文件中。该应用程序已在settings.py文件中注册。

对这里出了什么问题的任何帮助表示赞赏。

项目级别pres_value/urls.py：

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

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

应用级别present/urls.py：

from django.urls import path

from .views import HomePageView, PresentValueView, AboutPageView, ResultView

urlpatterns = [
    path('', HomePageView.as_view(), name='home'),
    path('about/', AboutPageView.as_view(), name='about'),
    path('pv/', PresentValueView.as_view(), name='present_value'),
    path('result/', ResultView.as_view(), name='result'),
]

settings.py：

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

目录结构：

??? Pipfile
??? Pipfile.lock
??? db.sqlite3
??? manage.py
??? pres_value
?   ??? __init__.py
?   ??? __pycache__
?   ??? settings.py
?   ??? urls.py
?   ??? wsgi.py
??? present
?   ??? __init__.py
?   ??? __pycache__
?   ??? admin.py
?   ??? apps.py
?   ??? forms.py
?   ??? migrations
?   ?   ??? 0001_initial.py
?   ?   ??? __init__.py
?   ?   ??? __pycache__
?   ??? models.py
?   ??? templates
?   ?   ??? present
?   ?       ??? about.html
?   ?       ??? home.html
?   ?       ??? pv.html
?   ?       ??? result.html
?   ??? tests.py
?   ??? urls.py
?   ??? views.py
??? templates
    ??? base.html
    ??? footer.html
    ??? header.html
    ??? nav.html

views.py

from django.shortcuts import reverse
from django.views.generic import TemplateView
from django.views.generic.edit import CreateView
from .forms import PresentForm
from .models import PresentValue

# Create your views here.
class HomePageView(TemplateView):
    template_name = 'present/home.html'

class PresentValueView(CreateView):
    model = PresentValue
    template_name = 'present/pv.html'
    # fields = ['first', 'second']
    success_url = reverse('result')

class AboutPageView(TemplateView):
    template_name = 'present/about.html'  ## this is where I show an error

class ResultView(TemplateView):
    template_name = 'present/result.html'

Answer 1

循环导入是由reverse().

解决方法：使用reverse_lazy.

from django.core.urlresolvers import reverse_lazy

class PresentValueView(CreateView):
    model = PresentValue
    template_name = 'present/pv.html'
    # fields = ['first', 'second']
    success_url = reverse_lazy('result')