Django Gotchas

Django hows

How Django manages Url's?

It only needs a module for url configs, which will be a simple mapping between URL patterns to python functions corresponding to views.

from django.conf.urls import url
 
from . import views
 
urlpatterns = [
    url(r'^articles/2003/$', views.special_case_2003),
    url(r'^articles/([0-9]{4})/$', views.year_archive),
    url(r'^articles/([0-9]{4})/([0-9]{2})/$', views.month_archive),
    url(r'^articles/([0-9]{4})/([0-9]{2})/([0-9]+)/$', views.article_detail),
]

To capture a value from the URL, just put parenthesis around it. Example requests: A request to /articles/2005/03/ would match the third entry in the list. Django would call the function views.month_archive(request, '2005', '03').
/articles/2005/3/ would not match any URL patterns, because the third entry in the list requires two digits for the month.
/articles/2003/ would match the first pattern in the list, not the second one, because the patterns are tested in order, and the first one is the first test to pass.
/articles/2003 would not match any of these patterns, because each pattern requires that the URL end with a slash. /articles/2003/03/03/ would match the final pattern. Django would call the function views.article_detail(request, '2003', '03', '03').

You can name the variables like this:

urlpatterns = [
    url(r'^articles/2003/$', views.special_case_2003),
    url(r'^articles/(?P<year>[0-9]{4})/$', views.year_archive),
    url(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/$', views.month_archive),
    url(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/(?P<day>[0-9]{2})/$', views.article_detail),
]

The URLconf doesn’t look at the request method. In other words, all request methods – POST, GET, HEAD, etc. – will be routed to the same function for the same URL.

You can specify default values:

urlpatterns = [
    url(r'^blog/$', views.page),
    url(r'^blog/page(?P<num>[0-9]+)/$', views.page),
]
 
def page(request, num="1"):
    # Output the appropriate page of blog entries, according to num.
    ...

At any point, your urlpatterns can “include” other URLconf modules. This essentially “roots” a set of URLs below other ones.

urlpatterns = [
    # ... snip ...
    url(r'^community/', include('django_website.aggregator.urls')),
    url(r'^contact/', include('django_website.contact.urls')),
    # ... snip ...
]

Note that the regular expressions in this example don’t have a $ (end-of-string match character) but do include a trailing slash. Whenever Django encounters include() (django.conf.urls.include()), it chops off whatever part of the URL matched up to that point and sends the remaining string to the included URLconf for further processing.

extra_patterns = [
    url(r'^reports/$', credit_views.report),
    url(r'^reports/(?P<id>[0-9]+)/$', credit_views.report),
    url(r'^charge/$', credit_views.charge),
]
 
urlpatterns = [
    url(r'^$', main_views.homepage),
    url(r'^help/', include('apps.help.urls')),
    url(r'^credit/', include(extra_patterns)),
]

We can write some url patterns in several ways:

urlpatterns = [
    url(r'^(?P<page_slug>[\w-]+)-(?P<page_id>\w+)/history/$', views.history),
    url(r'^(?P<page_slug>[\w-]+)-(?P<page_id>\w+)/edit/$', views.edit),
    url(r'^(?P<page_slug>[\w-]+)-(?P<page_id>\w+)/discuss/$', views.discuss),
    url(r'^(?P<page_slug>[\w-]+)-(?P<page_id>\w+)/permissions/$', views.permissions),
]
 
urlpatterns = [
    url(r'^(?P<page_slug>[\w-]+)-(?P<page_id>\w+)/', include([
        url(r'^history/$', views.history),
        url(r'^edit/$', views.edit),
        url(r'^discuss/$', views.discuss),
        url(r'^permissions/$', views.permissions),
    ])),
]

You can send extra options:

urlpatterns = [
    url(r'^blog/(?P<year>[0-9]{4})/$', views.year_archive, {'foo': 'bar'}),
]

In this example, for a request to /blog/2005/, Django will call views.year_archive(request, year='2005', foo='bar'). You can send extra parameters:

urlpatterns = [
    url(r'^blog/', include('inner')),
]
 
 
urlpatterns = [
    url(r'^archive/$', views.archive, {'blogid': 3}),
    url(r'^about/$', views.about, {'blogid': 3}),
]

URL namespaces

A URL namespace comes in two parts, both of which are strings:

Application namespace: This describes the name of the application that is being deployed.
Instance namespace: This identifies a specific instance of an application and should be unique across your entire project.

Namespaced URLs are specified using the ':' operator. For example, the main index page of the admin application is referenced using 'admin:index'. This indicates a namespace of 'admin', and a named URL of 'index'. Namespaces can also be nested. The named URL 'sports:polls:index' would look for a pattern named 'index' in the namespace 'polls' that is itself defined within the top-level namespace 'sports'.