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CE419 Web Programming
Session 13: Django Web Framework: Views
Review
- Model—Template—View architecture
CE419 Session 13: Django Web Framework: Views Web Programming - - PowerPoint PPT Presentation
CE419 Session 13: Django Web Framework: Views Web Programming - - PowerPoint PPT Presentation
CE419 Session 13: Django Web Framework: Views Web Programming Review ModelTemplateView architecture Views and URLconfs Django has the concept of views to encapsulate the logic responsible for processing a users request and for
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Views and URLconfs
- Django has the concept of views to encapsulate the
logic responsible for processing a user’s request and for returning the response.
- Comparison with the CGI example (random number
generator).
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Writing Views
- A view function, or view for short, is simply a Python
function that takes a Web request and returns a Web response.
from django.http import HttpResponse import datetime def current_datetime(request): now = datetime.datetime.now() html = "<html><body>It is now %s.</body></html>" % now return HttpResponse(html)
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URLconfs
- Fire up the built-in web server!
- Where is my view?!
~/myblog $ python manage.py runserver
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URLconfs (cont'd)
- Remember HTTP requests?
- We need a way to map a path to a view.
- When the user requests for a path, Django finds the
corresponding view and executes it.
GET /now/ HTTP/1.1 Host: mail.ce.sharif.edu Referer: http://mail.ce.sharif.edu/ Content-Length: 125
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URLconfs (cont'd)
- To hook a view function to a particular URL with Django,
use a URLconf.
- A URLconf is like a table of contents for your Django-
powered Web site.
- “For this URL, call this code, and for that URL, call that
code.”
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URLconfs (cont'd)
myblog/ ├── manage.py └── myblog ├── __init__.py ├── settings.py ├── urls.py └── wsgi.py
from django.conf.urls import include, url from django.contrib import admin urlpatterns = [ url(r'^now/$', 'posts.views.current_datetime'), url(r'^login/$', 'users.views.login'), url(r'^admin/', include(admin.site.urls)), ]
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URLconfs (cont'd)
- What the URLconf searches against?
- The URLconf searches against the requested URL, as
a normal Python string. This does not include GET or POST parameters, or the domain name.
http://www.example.com/myapp/?page=3 myapp/
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URL Patterns
- Not are URLs are that simple.
- We can use Regular Expressions to capture these.
https://www.facebook.com/groups/390233697744819/ http://www.imdb.com/title/tt0816692/ https://twitter.com/Arsenal/status/107858262212358144 https://itunes.apple.com/us/genre/ios-business/id6000 http://www.last.fm/user/johndoe/now ^groups/(\d+)/$ ^title/tt(\d+)/$ ^(?P<username>\w+)/status/(?P<tweet_id>\d+)$
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Let's see 'regular expressions' in action.
Showtime!
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Capture Values
- To capture a value from the URL, just put parenthesis
around it.
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), ]
http://www.example.com/articles/2014/12/ month_archive(request, '2014', '12')
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Capture Values (cont'd)
- The previous example used simple, non-named regular-
expression groups (via parenthesis) to capture bits of the URL and pass them as positional arguments to 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.
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Capture Values (cont'd)
- In Python regular expressions, the syntax for named
regular-expression groups is (?P<name>pattern)
- Captured arguments are always strings.
url(r'^articles/(?P<year>[0-9]{4})/(?P<month>[0-9]{2})/$', views.month_archive),
http://www.example.com/articles/2014/12/ month_archive(request, year='2014', month='12')
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Including other URLconfs
- Why is it useful?
- 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(), it chops off
whatever part of the URL matched up to that point.
from django.conf.urls import include, url urlpatterns = [ url(r'^community/', include('django_website.aggregator.urls')), url(r'^contact/', include('django_website.contact.urls')), ]
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Let's go back to views!
- When a page is requested, Django creates an
HttpRequest object that contains metadata about the request.
from django.http import HttpResponse import datetime def current_datetime(request): now = datetime.datetime.now() html = "<html><body>It is now %s.</body></html>" % now return HttpResponse(html)
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HttpRequest Class
- HttpRequest.scheme
- HttpRequest.path
- HttpRequest.method
- HttpRequest.GET (django.http.QueryDict object)
- HttpRequest.POST (django.http.QueryDict object)
- HttpRequest.COOKIES
- HttpRequest.META
- and a bunch of other things!
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HttpResponse Class
- In contrast to HttpRequest objects, which are created
automatically by Django, HttpResponse objects are your responsibility.
- Typical usage is to pass the contents of the page, as a
string, to the HttpResponse constructor:
from django.http import HttpResponse response = HttpResponse("Here's the text of the Web page.") response = HttpResponse("Not found, man.", status=404) response = HttpResponse("Text only, please.", content_type="text/html") response['User-Custom-Header'] = 'Custom Value'
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HttpResponse Subclasses
- HttpResponseRedirect
- HttpResponsePermanentRedirect
- HttpResponseBadRequest
- HttpResponseNotFound
- HttpResponseForbidden
- HttpResponseServerError
- JsonResponse
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Let's see 'views' in action!
Showtime!
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Any questions?
Thank you.
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