The Django Web Application Framework
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The Django Web Application Framework Simon Willison http://simonwillison.net/ ACCU, Python Track, 20th April 2006
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Slides from a talk given to the ACCU Python Track in Oxford, on the 20th April 2006.
Transcript of The Django Web Application Framework
The Django Web Application Framework
Simon Willisonhttp://simonwillison.net/
ACCU, Python Track, 20th April 2006
This talk
An overview of Django
What's in a web framework, anyway?
Framework comparison
(and some pretty screenshots, too)
Origins
Lawrence, Kansas - 2003
Web development on Journalism deadlines
... in three days
The ideal framework...Clean URLs
Loosely coupled components
Designer-friendly templates
As little code as possible
Really fast development
We didn’t mean to build a framework...
... but nothing else really fitted the bill
Building a framework
HTTP handling
HTTP/1.1 200 OKDate: Wed, 19 Apr 2006 23:53:29 GMTServer: ApacheVary: CookieConnection: closeContent-Type: text/html; charset=utf-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1- transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> [...]
GET /community/ HTTP/1.0Host: www.djangoproject.com
Parse the request; generate a response
GET variables, POST variables, cookies,
uploaded files, caching, content
negotiation
HttpRequestHttpResponse
def index(request): s = “Hello, World” return HttpResponse(s)
def index(request): r = HttpResponse( mimetype='text/plain' ) r.write(“Hello, World”) return r
def index(request): if request.GET: s = “Hi, %s” % \ escape(request.GET.get( ’name’, ‘anon’) else: s = “Hello, World” return HttpResponse(s)
URL dispatching
http://www.example.com/poll/5/
What code shall we execute?
urlpatterns = patterns('', (r'^$', 'views.index'), (r'^hello/', ‘views.hello'), (r'^poll/(\d+)/', ‘views.poll'),)
Database access
...(r'^poll/(\d+)/', 'views.poll'),...
def poll(request, poll_id): poll = Poll.objects.get( pk=poll_id ) return HttpResponse( 'Title: ' + poll.title )
class Poll(Model): question = CharField(maxlength=200) pub_date = DateTimeField('date published')
class Choice(Model): poll = ForeignKey(Poll) choice = CharField(maxlength=200) votes = IntegerField()
BEGIN;CREATE TABLE "polls_poll" ( "id" serial NOT NULL PRIMARY KEY, "question" varchar(200) NOT NULL, "pub_date" timestamp with time zone NOT NULL);CREATE TABLE "polls_choice" ( "id" serial NOT NULL PRIMARY KEY, "poll_id" integer NOT NULL REFERENCES "polls_polls" ("id"), "choice" varchar(200) NOT NULL, "votes" integer NOT NULL);COMMIT;
p = Poll( question = "What's up?", pub_date = datetime.now())p.save()
>>> p.id1
>>> p.question"What's up?"
>>> p.pub_datedatetime(2005, 7, 15, 12, 00, 53)
Templating
Gluing strings together gets old fast
{ 'today': datetime.date.today(), 'edibles': ['pear', 'apple', 'orange']}
<h1>Hello World!</h1>
<p>Today is {{ today|date:”jS F, Y” }}</p>
{% if edibles %}<ul> {% for fruit in edibles %} <li>{{ fruit }}</li> {% endfor %}</ul>{% endif %}
<h1>Hello World!</h1>
<p>Today is 20th April, 2006</p>
<ul> <li>pear</li> <li>apple</li> <li>orange</li></ul>
def hello(request): t = get_template('hello.html') c = Context({ 'today': datetime.date.today(), 'edibles': ['pear', 'apple', 'orange'] }) return HttpResponse(t.render(c))
All you really need are variables, conditionals
and loops
HTTP handling
URL dispatching
Templating
Documentation
Database access (optional)
... no wonder there are so many frameworks!
Essential ingredients
Extras
Forms are boring
1. Display form
2. Validate submitted data
3. If errors, redisplay with:
3.1. Contextual error messages
3.2. Correct fields pre-filled
4. ... do something useful!
Model validation rules + the Manipulator API
do all of this for you
django.contrib.admin does even more
class Poll(Model): question = CharField(maxlength=200) pub_date = DateTimeField('date published') class Admin: list_display = ('question', 'pub_date')
class Choice(Model): poll = ForeignKey(Poll) choice = CharField(maxlength=200) votes = IntegerField() class Admin: pass
Smarter templating
Common headers and footers?
Template inheritance
base.html<html><head><title> {% block title %}{% endblock %}
</title></head><body>{% block main %}{% endblock %}
<div id=”footer”>{% block footer %}(c) 2006{% endblock %}<div></body></html>
home.html
{% extends “base.html” %}{% block title %}Homepage{% endblock %}
{% block main %}
Main page contents goes here.{% endblock %}
combined<html><head><title> Homepage</title></head><body>Main page contents goes here.
<div id=”footer”>(c) 2006<div></body></html>
Custom template tags
{{ page.content|textile }}
{{ page.content|textile }}
{% comment_form for news.stories story.id with is_public yes photos_optional thumbs,200,400 ratings_optional scale:1-5|first_option|second_option %}
from django import template
register = template.Library()
def textile(value): try: import textile except ImportError: return value else: return textile.textile(value)
register.filter(textile)
i18n and l10n
BengaliCzechWelshDanishGermanGreekEnglishSpanishFrenchGalicianHebrewIcelandicItalian
JapaneseDutch
NorwegianBrazilian
RomanianRussianSlovak
SlovenianSerbianSwedish
UkrainianSimplified ChineseTraditional Chinese
Authentication and authorisation
Community
?
It’s a matter of taste
HTTP handlingWhat happens to form variables? GET vs POST
How to handle /path?foo=1&foo=2
How to send back non-standard responses
Different Content-Type (and other) headers
404s, 500s
Session support?
URL dispatching
Object traversal or explicit configuration?
Reversible URLs?
Parameter extraction
Trailing slashes?
Database handling
To ORM or not to ORM?
Pluralisation?
Handling joins
Lookup syntax
When should you fall back on raw SQL?
TemplatingPlain text or XML?
Markup visible on the page or hidden in HTML attributes?
Logic in the template vs logic in the view/controller
Safe (and limited) or unsafe (and more powerful)
Language extension mechanism?
Where’s the line?
Authentication and authorisation?
Automated admin / forms?
i18n and l10n?
JavaScript and Ajax?
Getting involved
Summer of Code 2006
Extra slides
Comparisons
HTTP$_GET, $_POST, $_REQUEST etc
URL dispatch Filesystem
Database handling mysql_* functions
Templating <?php ... ?>
HTTP CherryPy
URL dispatchObject path
traversal
Database handling SQLObject
TemplatingKid (XML), common
templating API
HTTP ActionController?
URL dispatchObject traversal,
Routes
Database handling ActiveRecord
Templating ERb, Builder, RJS
