the django web application framework

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Slide 1: The Django Web Application Framework Simon Willison http://simonwillison.net/ ACCU, Python Track, 20th April 2006 Slide 2: This talk An overview of Django What's in a web framework, anyway? Framework comparison (and some pretty screenshots, too) Slide 3: Origins Slide 4: Lawrence, Kansas - 2003 Slide 10: Web development on Journalism deadlines Slide 15: ... in three days Slide 16: The ideal framework... Clean URLs Loosely coupled components Designer-friendly templates As little code as possible Really fast development Slide 17: We didn’t mean to build a framework... Slide 18: ... but nothing else really fitted the bill Slide 19: Building a framework Slide 20: HTTP handling Slide 21: GET /community/ HTTP/1.0 Host: www.djangoproject.com HTTP/1.1 200 OK Date: Wed, 19 Apr 2006 23:53:29 GMT Server: Apache Vary: Cookie Connection: close Content-Type: text/html; charset=utf-8 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> [...] Slide 22: Parse the request; generate a response Slide 23: GET variables, POST variables, cookies, uploaded files, caching, content negotiation Slide 24: HttpRequest HttpResponse Slide 25: def index(request): s = “Hello, World” return HttpResponse(s) Slide 26: def index(request): r = HttpResponse( mimetype='text/plain' ) r.write(“Hello, World”) return r Slide 27: def index(request): if request.GET: s = “Hi, %s” % \ escape(request.GET.get( ’name’, ‘anon’) else: s = “Hello, World” return HttpResponse(s) Slide 28: URL dispatching Slide 29: http://www.example.com/poll/5/ What code shall we execute? Slide 30: urlpatterns = patterns('', (r'^$', 'views.index'), (r'^hello/', ‘views.hello'), (r'^poll/(\d+)/', ‘views.poll'), ) Slide 31: Database access Slide 32: ... (r'^poll/(\d+)/', 'views.poll'), ... def poll(request, poll_id): poll = Poll.objects.get( pk=poll_id ) return HttpResponse( 'Title: ' + poll.title ) Slide 33: class Poll(Model): question = CharField(maxlength=200) pub_date = DateTimeField('date published') class Choice(Model): poll = ForeignKey(Poll) choice = CharField(maxlength=200) votes = IntegerField() Slide 34: 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; Slide 35: p = Poll( question = "What's up?", pub_date = datetime.now() ) p.save() Slide 36: >>> p.id 1 >>> p.question "What's up?" >>> p.pub_date datetime(2005, 7, 15, 12, 00, 53) Slide 37: Templating Slide 38: Gluing strings together gets old fast Slide 39: { 'today': datetime.date.today(), 'edibles': ['pear', 'apple', 'orange'] } Slide 40: <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 %} Slide 41: <h1>Hello World!</h1> <p>Today is 20th April, 2006</p> <ul> <li>pear</li> <li>apple</li> <li>orange</li> </ul> Slide 42: def hello(request): t = get_template('hello.html') c = Context({ 'today': datetime.date.today(), 'edibles': ['pear', 'apple', 'orange'] }) return HttpResponse(t.render(c)) Slide 43: All you really need are variables, conditionals and loops Slide 44: Essential ingredients HTTP handling URL dispatching Templating Documentation Database access (optional) ... no wonder there are so many frameworks! Slide 45: Extras Slide 46: Forms are boring Slide 47: 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! Slide 48: Model validation rules + the Manipulator API do all of this for you Slide 49: django.contrib.admin does even more Slide 51: 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 Slide 52: Smarter templating Slide 53: Common headers and footers? Slide 54: Template inheritance Slide 55: 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> Slide 56: home.html {% extends “base.html” %} {% block title %}Homepage{% endblock %} {% block main %} Main page contents goes here. {% endblock %} Slide 57: combined <html> <head> <title> Homepage </title> </head> <body> Main page contents goes here. <div id=”footer”> (c) 2006 <div> </body> </html> Slide 58: Custom template tags Slide 60: {{ page.content\|textile }} Slide 61: {{ 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 %} Slide 62: 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) Slide 63: i18n and l10n Slide 65: Bengali Czech Welsh Danish German Greek English Spanish French Galician Hebrew Icelandic Italian Japanese Dutch Norwegian Brazilian Romanian Russian Slovak Slovenian Serbian Swedish Ukrainian Simpliﬁed Chinese Traditional Chinese Slide 66: Authentication and authorisation Slide 67: Community Slide 68: ? Slide 69: It’s a matter of taste Slide 70: HTTP handling What 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? Slide 71: URL dispatching Object traversal or explicit configuration? Reversible URLs? Parameter extraction Trailing slashes? Slide 72: Database handling To ORM or not to ORM? Pluralisation? Handling joins Lookup syntax When should you fall back on raw SQL? Slide 73: Templating Plain 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? Slide 74: Where’s the line? Authentication and authorisation? Automated admin / forms? i18n and l10n? JavaScript and Ajax? Slide 75: Getting involved Slide 78: Summer of Code 2006 Slide 79: www.djangoproject.com Slide 81: Extra slides Slide 82: Comparisons Slide 84: HTTP URL dispatch Database handling Templating $_GET, $_POST, $_REQUEST etc Filesystem mysql_* functions <?php ... ?> Slide 86: HTTP URL dispatch Database handling Templating CherryPy Object path traversal SQLObject Kid (XML), common templating API Slide 88: HTTP URL dispatch Database handling Templating ActionController? Object traversal, Routes ActiveRecord ERb, Builder, RJS