Allowing student project review page to be viewed in read-only mode after the deadline has passed.
Patch by: Lennard de Rijk
Reviewed by: to-be-reviewed
==============URL dispatcher==============A clean, elegant URL scheme is an important detail in a high-quality Webapplication. Django lets you design URLs however you want, with no frameworklimitations.There's no ``.php`` or ``.cgi`` required, and certainly none of that``0,2097,1-1-1928,00`` nonsense.See `Cool URIs don't change`_, by World Wide Web creator Tim Berners-Lee, forexcellent arguments on why URLs should be clean and usable... _Cool URIs don't change: http://www.w3.org/Provider/Style/URIOverview========To design URLs for an app, you create a Python module informally called a**URLconf** (URL configuration). This module is pure Python code andis a simple mapping between URL patterns (as simple regular expressions) toPython callback functions (your views).This mapping can be as short or as long as needed. It can reference othermappings. And, because it's pure Python code, it can be constructeddynamically.How Django processes a request==============================When a user requests a page from your Django-powered site, this is thealgorithm the system follows to determine which Python code to execute: 1. Django looks at the ``ROOT_URLCONF`` setting in your `settings file`_. This should be a string representing the full Python import path to your URLconf. For example: ``"mydjangoapps.urls"``. 2. Django loads that Python module and looks for the variable ``urlpatterns``. This should be a Python list, in the format returned by the function ``django.conf.urls.defaults.patterns()``. 3. Django runs through each URL pattern, in order, and stops at the first one that matches the requested URL. 4. Once one of the regexes matches, Django imports and calls the given view, which is a simple Python function. The view gets passed a `request object`_ as its first argument and any values captured in the regex as remaining arguments... _settings file: ../settings/.. _request object: ../request_response/#httprequest-objectsExample=======Here's a sample URLconf:: from django.conf.urls.defaults import * urlpatterns = patterns('', (r'^articles/2003/$', 'news.views.special_case_2003'), (r'^articles/(\d{4})/$', 'news.views.year_archive'), (r'^articles/(\d{4})/(\d{2})/$', 'news.views.month_archive'), (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'news.views.article_detail'), )Notes: * ``from django.conf.urls.defaults import *`` makes the ``patterns()`` function available. * To capture a value from the URL, just put parenthesis around it. * There's no need to add a leading slash, because every URL has that. For example, it's ``^articles``, not ``^/articles``. * The ``'r'`` in front of each regular expression string is optional but recommended. It tells Python that a string is "raw" -- that nothing in the string should be escaped. See `Dive Into Python's explanation`_.Example requests: * A request to ``/articles/2005/03/`` would match the third entry in the list. Django would call the function ``news.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. Feel free to exploit the ordering to insert special cases like this. * ``/articles/2003`` would not match any of these patterns, because each pattern requires that the URL end with a slash. * ``/articles/2003/03/3/`` would match the final pattern. Django would call the function ``news.views.article_detail(request, '2003', '03', '3')``... _Dive Into Python's explanation: http://diveintopython.org/regular_expressions/street_addresses.html#re.matching.2.3Named groups============The above example used simple, *non-named* regular-expression groups (viaparenthesis) to capture bits of the URL and pass them as *positional* argumentsto a view. In more advanced usage, it's possible to use *named*regular-expression groups to capture URL bits and pass them as *keyword*arguments to a view.In Python regular expressions, the syntax for named regular-expression groupsis ``(?P<name>pattern)``, where ``name`` is the name of the group and``pattern`` is some pattern to match.Here's the above example URLconf, rewritten to use named groups:: urlpatterns = patterns('', (r'^articles/2003/$', 'news.views.special_case_2003'), (r'^articles/(?P<year>\d{4})/$', 'news.views.year_archive'), (r'^articles/(?P<year>\d{4})/(?P<month>\d{2})/$', 'news.views.month_archive'), (r'^articles/(?P<year>\d{4})/(?P<month>\d{2})/(?P<day>\d+)/$', 'news.views.article_detail'), )This accomplishes exactly the same thing as the previous example, with onesubtle difference: The captured values are passed to view functions as keywordarguments rather than positional arguments. For example: * A request to ``/articles/2005/03/`` would call the function ``news.views.month_archive(request, year='2005', month='03')``, instead of ``news.views.month_archive(request, '2005', '03')``. * A request to ``/articles/2003/03/3/`` would call the function ``news.views.article_detail(request, year='2003', month='03', day='3')``.In practice, this means your URLconfs are slightly more explicit and less proneto argument-order bugs -- and you can reorder the arguments in your views'function definitions. Of course, these benefits come at the cost of brevity;some developers find the named-group syntax ugly and too verbose.The matching/grouping algorithm-------------------------------Here's the algorithm the URLconf parser follows, with respect to named groupsvs. non-named groups in a regular expression:If there are any named arguments, it will use those, ignoring non-named arguments.Otherwise, it will pass all non-named arguments as positional arguments.In both cases, it will pass any extra keyword arguments as keyword arguments.See "Passing extra options to view functions" below.What the URLconf searches against=================================The URLconf searches against the requested URL, as a normal Python string. Thisdoes not include GET or POST parameters, or the domain name.For example, in a request to ``http://www.example.com/myapp/``, the URLconfwill look for ``/myapp/``.In a request to ``http://www.example.com/myapp/?page=3``, the URLconf will lookfor ``/myapp/``.The URLconf doesn't look at the request method. In other words, all requestmethods -- ``POST``, ``GET``, ``HEAD``, etc. -- will be routed to the samefunction for the same URL.Syntax of the urlpatterns variable==================================``urlpatterns`` should be a Python list, in the format returned by the function``django.conf.urls.defaults.patterns()``. Always use ``patterns()`` to createthe ``urlpatterns`` variable.Convention is to use ``from django.conf.urls.defaults import *`` at the top ofyour URLconf. This gives your module access to these objects:patterns--------A function that takes a prefix, and an arbitrary number of URL patterns, andreturns a list of URL patterns in the format Django needs.The first argument to ``patterns()`` is a string ``prefix``. See"The view prefix" below.The remaining arguments should be tuples in this format:: (regular expression, Python callback function [, optional dictionary])...where ``optional dictionary`` is optional. (See_`Passing extra options to view functions` below.)handler404----------A string representing the full Python import path to the view that should becalled if none of the URL patterns match.By default, this is ``'django.views.defaults.page_not_found'``. That defaultvalue should suffice.handler500----------A string representing the full Python import path to the view that should becalled in case of server errors. Server errors happen when you have runtimeerrors in view code.By default, this is ``'django.views.defaults.server_error'``. That defaultvalue should suffice.include-------A function that takes a full Python import path to another URLconf that shouldbe "included" in this place. See _`Including other URLconfs` below.Notes on capturing text in URLs===============================Each captured argument is sent to the view as a plain Python string, regardlessof what sort of match the regular expression makes. For example, in thisURLconf line:: (r'^articles/(?P<year>\d{4})/$', 'news.views.year_archive'),...the ``year`` argument to ``news.views.year_archive()`` will be a string, notan integer, even though the ``\d{4}`` will only match integer strings.A convenient trick is to specify default parameters for your views' arguments.Here's an example URLconf and view:: # URLconf urlpatterns = patterns('', (r'^blog/$', 'blog.views.page'), (r'^blog/page(?P<num>\d+)/$', 'blog.views.page'), ) # View (in blog/views.py) def page(request, num="1"): # Output the appropriate page of blog entries, according to num.In the above example, both URL patterns point to the same view --``blog.views.page`` -- but the first pattern doesn't capture anything from theURL. If the first pattern matches, the ``page()`` function will use itsdefault argument for ``num``, ``"1"``. If the second pattern matches,``page()`` will use whatever ``num`` value was captured by the regex.Performance===========Each regular expression in a ``urlpatterns`` is compiled the first time it'saccessed. This makes the system blazingly fast.The view prefix===============You can specify a common prefix in your ``patterns()`` call, to cut down oncode duplication.Here's the example URLconf from the `Django overview`_:: from django.conf.urls.defaults import * urlpatterns = patterns('', (r'^articles/(\d{4})/$', 'mysite.news.views.year_archive'), (r'^articles/(\d{4})/(\d{2})/$', 'mysite.news.views.month_archive'), (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'mysite.news.views.article_detail'), )In this example, each view has a common prefix -- ``'mysite.news.views'``.Instead of typing that out for each entry in ``urlpatterns``, you can use thefirst argument to the ``patterns()`` function to specify a prefix to apply toeach view function.With this in mind, the above example can be written more concisely as:: from django.conf.urls.defaults import * urlpatterns = patterns('mysite.news.views', (r'^articles/(\d{4})/$', 'year_archive'), (r'^articles/(\d{4})/(\d{2})/$', 'month_archive'), (r'^articles/(\d{4})/(\d{2})/(\d+)/$', 'article_detail'), )Note that you don't put a trailing dot (``"."``) in the prefix. Django putsthat in automatically... _Django overview: ../overview/Multiple view prefixes----------------------In practice, you'll probably end up mixing and matching views to the pointwhere the views in your ``urlpatterns`` won't have a common prefix. However,you can still take advantage of the view prefix shortcut to remove duplication.Just add multiple ``patterns()`` objects together, like this:Old:: from django.conf.urls.defaults import * urlpatterns = patterns('', (r'^/?$', 'django.views.generic.date_based.archive_index'), (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/$', 'django.views.generic.date_based.archive_month'), (r'^tag/(?P<tag>\w+)/$', 'weblog.views.tag'), )New:: from django.conf.urls.defaults import * urlpatterns = patterns('django.views.generic.date_based', (r'^/?$', 'archive_index'), (r'^(?P<year>\d{4})/(?P<month>[a-z]{3})/$','archive_month'), ) urlpatterns += patterns('weblog.views', (r'^tag/(?P<tag>\w+)/$', 'tag'), )Including other URLconfs========================At any point, your ``urlpatterns`` can "include" other URLconf modules. Thisessentially "roots" a set of URLs below other ones.For example, here's the URLconf for the `Django website`_ itself. It includes anumber of other URLconfs:: from django.conf.urls.defaults import * urlpatterns = patterns('', (r'^weblog/', include('django_website.apps.blog.urls.blog')), (r'^documentation/', include('django_website.apps.docs.urls.docs')), (r'^comments/', include('django.contrib.comments.urls.comments')), )Note that the regular expressions in this example don't have a ``$``(end-of-string match character) but do include a trailing slash. WheneverDjango encounters ``include()``, it chops off whatever part of the URL matchedup to that point and sends the remaining string to the included URLconf forfurther processing... _`Django website`: http://www.djangoproject.com/Captured parameters-------------------An included URLconf receives any captured parameters from parent URLconfs, sothe following example is valid:: # In settings/urls/main.py urlpatterns = patterns('', (r'^(?P<username>\w+)/blog/', include('foo.urls.blog')), ) # In foo/urls/blog.py urlpatterns = patterns('foo.views', (r'^$', 'blog.index'), (r'^archive/$', 'blog.archive'), )In the above example, the captured ``"username"`` variable is passed to theincluded URLconf, as expected.Passing extra options to view functions=======================================URLconfs have a hook that lets you pass extra arguments to your view functions,as a Python dictionary.Any URLconf tuple can have an optional third element, which should be adictionary of extra keyword arguments to pass to the view function.For example:: urlpatterns = patterns('blog.views', (r'^/blog/(?P<year>\d{4})/$', 'year_archive', {'foo': 'bar'}), )In this example, for a request to ``/blog/2005/``, Django will call the``blog.views.year_archive()`` view, passing it these keyword arguments:: year='2005', foo='bar'This technique is used in `generic views`_ and in the `syndication framework`_to pass metadata and options to views... _generic views: ../generic_views/.. _syndication framework: ../syndication/.. admonition:: Dealing with conflicts It's possible to have a URL pattern which captures named keyword arguments, and also passes arguments with the same names in its dictionary of extra arguments. When this happens, the arguments in the dictionary will be used instead of the arguments captured in the URL.Passing extra options to ``include()``--------------------------------------Similarly, you can pass extra options to ``include()``. When you pass extraoptions to ``include()``, *each* line in the included URLconf will be passedthe extra options.For example, these two URLconf sets are functionally identical:Set one:: # main.py urlpatterns = patterns('', (r'^blog/', include('inner'), {'blogid': 3}), ) # inner.py urlpatterns = patterns('', (r'^archive/$', 'mysite.views.archive'), (r'^about/$', 'mysite.views.about'), )Set two:: # main.py urlpatterns = patterns('', (r'^blog/', include('inner')), ) # inner.py urlpatterns = patterns('', (r'^archive/$', 'mysite.views.archive', {'blogid': 3}), (r'^about/$', 'mysite.views.about', {'blogid': 3}), )Note that extra options will *always* be passed to *every* line in the includedURLconf, regardless of whether the line's view actually accepts those optionsas valid. For this reason, this technique is only useful if you're certain thatevery view in the the included URLconf accepts the extra options you're passing.Passing callable objects instead of strings===========================================Some developers find it more natural to pass the actual Python function objectrather than a string containing the path to its module. This alternative issupported -- you can pass any callable object as the view.For example, given this URLconf in "string" notation:: urlpatterns = patterns('', (r'^archive/$', 'mysite.views.archive'), (r'^about/$', 'mysite.views.about'), (r'^contact/$', 'mysite.views.contact'), )You can accomplish the same thing by passing objects rather than strings. Justbe sure to import the objects:: from mysite.views import archive, about, contact urlpatterns = patterns('', (r'^archive/$', archive), (r'^about/$', about), (r'^contact/$', contact), )The following example is functionally identical. It's just a bit more compactbecause it imports the module that contains the views, rather than importingeach view individually:: from mysite import views urlpatterns = patterns('', (r'^archive/$', views.archive), (r'^about/$', views.about), (r'^contact/$', views.contact), )The style you use is up to you.Note that if you use this technique -- passing objects rather than strings --the view prefix (as explained in "The view prefix" above) will have no effect.