Slides

Web Development With Django
A Basic Introduction

Nick Efford
nick.efford@gmail.com
pythoneering.blogspot.com
twitter.com/python33r

School of Computing
University of Leeds

YPy Workshop, 11 December 2010

Nick Efford (Univ of Leeds) Web Development With Django YPy 2010-12-11 1 / 31

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

3 Front-End Development
Views
Templates


Introduction Setting Up

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



Files Required

1 Create a directory for this tutorial
2 Copy django.py and django-example.zip from the
USB drive to the new directory
3 Unpack the two archives



Files Required


Windows Users
Avoid spaces in pathnames!
Try unpacking Zip archives in C:tmppython or similar



Files Required


Windows Users
Avoid spaces in pathnames!
Try unpacking Zip archives in C:tmppython or similar

Note
We assume you have Python 2.6 or 2.7 already installed . . .



Setting Up Django

Do one of the following:
• In django-trunk directory (the one containing README) do
python setup.py install
• Set PYTHONPATH to include django-trunk directory

Use Python interpreter to verify:
>>> import django
>>> django.VERSION
(1, 3, 0, 'alpha', 1)


Introduction What Is Django?

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



What Is Django?

• High-level framework for rapid web development
• Complete stack of tools
• Data modelled with Python classes
• Production-ready data admin interface, generated dynamically
• Elegant system for mapping URLs to Python code
• ‘Generic views’ to handle common requests
• Clean, powerful template language
• Components for user authentication, form handling, caching . . .



A Working Example

Football match results and league tables


Getting Started Project Structure

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



Project Structure
Project
• A Python package on your PYTHONPATH
• Holds project-wide settings in settings.py
• Holds a URL conﬁguration (URLconf) in urls.py
• Contains or references one or more apps

App
• A Python package on your PYTHONPATH
(typically created as a subpackage of the project itself)
• May contain data models in models.py
• May contain views in views.py
• May have its own URL conﬁguration in urls.py



Creating Projects & Apps

Creating a project:
django-admin.py startproject football

Creating an app within a project directory:
cd football
./manage.py startapp club



Up & Running

1 Set PYTHONPATH to include parent of your project directory
2 Deﬁne new environment variable DJANGO_SETTINGS_MODULE,
setting it to project settings (football.settings)
3 Try running the development server:
./manage.py runserver



settings.py
• Database used (PostgreSQL, MySQL, Oracle, SQLite . . . )
• Which apps & middleware components are active
• Paths to templates and static media
• How logging is done . . .



settings.py
• Database used (PostgreSQL, MySQL, Oracle, SQLite . . . )
• Which apps & middleware components are active
• Paths to templates and static media
• How logging is done . . .

DATABASES = {
'default': {
'ENGINE': 'django.db.backends.sqlite3',
'NAME' : os.path.join(os.path.dirname(__file__), 'football.db'),
...
}
}
...
INSTALLED_APPS = (
...
'django.contrib.admin',
'football.club',
)


Getting Started Data Handling

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



The Data Model

• A description of database layout, as a Python class
• Normally represents one database table
• Has ﬁelds that map onto columns of the table
• Many built-in ﬁeld types
• CharField, TextField
• IntegerField, FloatField, DecimalField
• DateField, DateTimeField, TimeField
• EmailField, URLField
• ForeignKey . . .



Example

from django.db import models

class Club(models.Model):
"""A football club."""

name = models.CharField(max_length=30)
year_established = models.PositiveSmallIntegerField()
ground = models.CharField(max_length=30)

class Meta:
ordering = ('name',)

def __unicode__(self):
return self.name



Creating The Database

1 Optionally check table creation SQL:
./manage.py sql club
2 Sync installed apps with database:
./manage.py syncdb
3 Optionally check the outcome in the database:
./manage.py dbshell
4 Populate the database



Creating & Saving Objects

Invoke constructor and call save method:
club = Club(name='Arsenal', year_established=1886,
ground='Emirates Stadium')

club.save()



Creating & Saving Objects

Invoke constructor and call save method:
club = Club(name='Arsenal', year_established=1886,

club.save()

. . . or call create method of Club model manager:
Club.objects.create(name='Arsenal', year_established=1886,



Retrieving Objects

Retrieve a single object with get:
club = Club.objects.get(name='Liverpool')



Retrieving Objects

Retrieve a single object with get:
club = Club.objects.get(name='Liverpool')

Retrieve querysets with all, filter, etc:
for club in Club.objects.all():
print club

for club in Club.objects.filter(year_established=1878):
print club


Getting Started The Admin Interface

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



Registering Models
In admin.py in the club app:
from django.contrib import admin
from football.club.models import Club

admin.site.register(Club)



Registering Models
In admin.py in the club app:

admin.site.register(Club)

In top-level urls.py:
admin.autodiscover()

urlpatterns = patterns('',
(r'^admin/', include(admin.site.urls)),
(r'^clubs/', include('football.club.urls')),
...
)



The Admin Interface


Front-End Development Views

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



Generic Views

Provide ready-made logic for many common tasks:
• Issuing a redirect
• Displaying a paginated list of objects
• Displaying a ‘detail’ page for a single object
• Yearly, monthly or daily listing of date-based objects
• ‘Latest items’ page for date-based objects
• Object creation, updating, deletion (with/without authorisation)



Generic Views Example
views.py
from django.views.generic import ListView

class ClubListView(ListView):
model = Club
context_object_name = 'clubs'



Generic Views Example
views.py
from django.views.generic import ListView

class ClubListView(ListView):
model = Club
context_object_name = 'clubs'

urls.py
from django.conf.urls.defaults import *
from football.club.views import ClubListView

urlpatterns = patterns('',
(r'^$', ClubListView.as_view()),
...
)



View Function
• Takes an HTTPRequest object as a parameter
• Returns an HTTPResponse object to caller
• Is associated with a particular URL via the URLconf



View Function

from datetime import date
from django.http import HttpResponse

def today(request):
html = '<html><body><h2>%s</h2></body></html>' % date.today()
return HttpResponse(html)



View Function

from datetime import date
from django.http import HttpResponse

def today(request):
html = '<html><body><h2>%s</h2></body></html>' % date.today()
return HttpResponse(html)

from django.shortcuts import render_to_response

def clubs(request):
data = { 'clubs': Club.objects.all() }
return render_to_response('clubs.html', data)


Front-End Development Templates

Outline

1 Introduction
Setting Up
What Is Django?

2 Getting Started
Project Structure
Data Handling
The Admin Interface

Views
Templates



Templates
Text files containing
• Variables, replaced by values when the template is rendered
{{ today }}
• Filters that modify how values are displayed
{{ today|date:"D d M Y" }}
• Tags that control the logic of the rendering process
{% if name == "nick" %}
<p>Hello, Nick!</p>
{% else %}
<p>Who are you?</p>
{% endif %}

Django comes with a large collection of useful tags & filters, and you
can also define your own . . .



Template Example
settings.py
TEMPLATE_DIRS = (
os.path.join(os.path.dirname(__file__), 'templates'),
)



Template Example
settings.py
TEMPLATE_DIRS = (
os.path.join(os.path.dirname(__file__), 'templates'),
)

templates/club/club_list.html
{% extends "base.html" %}
{% block title %}Clubs{% endblock %}
{% block content %}
<h1>Clubs</h1>
<ol>
{% for club in clubs %}
<li>{{ club }}</li>
{% endfor %}
</ol>
{% endblock %}


Final Thoughts

Summary

We have shown you
• The structure of a Django project
• How models represent data in Django applications
• How data can be stored and queried via model instances
• How data can be managed through a dynamic admin interface
• How functionality is represent by views, each associated
with URLs that match a given pattern
• How views render a response using a template


Final Thoughts

Summary

We have shown you
• The structure of a Django project
• How models represent data in Django applications
• How data can be stored and queried via model instances
• How data can be managed through a dynamic admin interface
• How functionality is represent by views, each associated
with URLs that match a given pattern
• How views render a response using a template

Hopefully, you now have a sense of what it is like
to develop web applications in Django!


Final Thoughts

Finding Out More

• Project home
http://www.djangoproject.com/
• Sites built using Django
http://djangosites.org/
• Django developers
http://djangopeople.net/
• Django-based rapid development platform
http://pinaxproject.com/
• Apress books (http://www.apress.com/)
• The Deﬁnitive Guide to Django (2nd edition)
• Practical Django Projects (2nd edition)
• Pro Django
• Beginning Django E-Commerce


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