Q:

`Page not found` though the urls are designed carefully

My minimal project has worked smoothly for days, but throw page not found error abruptly just now.
I double checked the urls but am unable to locate the error. 
the request is http://127.0.0.1:8001/user/login/
Page not found (404)
Request Method: GET
Request URL:    http://127.0.0.1:8001/user/login/
Using the URLconf defined in forum.urls, Django tried these URL patterns, in this order:

^admin/
^$ [name='index']
^article/
^user/ ^register$ [name='register']
^user/ ^activate/(?P<a_code>\w+)$ [name='activate']
^user/ ^login$ [name='login']
^user/ ^logout$ [name='logout']
The current path, user/login/, didn't match any of these.

The  app user.urls:
from django.conf.urls import url
from django.contrib.auth import urls
from django.contrib.auth.views import login, logout

from . import views

# User app's url

urlpatterns = [
    # show the register page
    url(r"^register$", views.register, name="register"),
    #activate the user account from the registered email
    url(r"^activate/(?P<a_code>\w+)$", views.activate, name="activate"),
    # Log in page, override the default registration/login.html
    url(r"^login$", login, {"template_name":"user/login.html"},name="login"),
    url(r"^logout$", logout, {"template_name":""},name="logout"),
]

The top level urls.py
from django.conf.urls import url,include
from django.contrib import admin

from article import views
# Project url
urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r"^$", views.index, name="index"),
    url(r'^article/', include('article.urls',namespace='article')),
    url(r'^user/', include('user.urls',namespace='user')),
]

The templates:
└── user
    ├── activate.html
    ├── failure.html
    ├── login.html
    ├── register.html
    ├── success.html
    └── validate.html

1 directory, 6 files

What's the problem might be?

A:

Looks like the problem is related to appended slash, try to add slash at the end of the patter:
url(r"^login/$", login, {"template_name":"user/login.html"},name="login"),

You may also disable APPEND_SLASH in project settings.

