Introduction To Django (Strange Loop 2011)

Introduction to Django

Jacob Kaplan-Moss

Strange Loop 2011
http://lanyrd.com/sfypm

Django Training

Part 1: Introduction to Django.

“Django is a high-level
Python web framework
that encourages rapid
development and clean,

”
pragmatic design.

2


”
pragmatic design.

3


”
pragmatic design.

4


”
pragmatic design.

5

Documentation
http://django.me/design
http://www.djangobook.com/en/2.0/chapter01/

6

Which Django version
should I use?

7

Installing Django

• Download and run http://bit.ly/dsetup
(http://python-‐distribute.org/distribute_setup.py)

• easy_install Django
• Later: learn about pip and virtualenv
http://pip.rtfd.org/
http://virtualenv.rtfd.org/

8

$ django-‐admin.py startproject yabl

10

yabl/
__init__.py
manage.py
settings.py
urls.py

11

$ python manage.py runserver
Validating models...
0 errors found.

Django version 1.1 beta 1 SVN-‐10844, using settings 'yabl.settings'
Development server is running at http://127.0.0.1:8000/
Quit the server with CONTROL-‐C.

12

Project settings

• DATABASE_ENGINE
• DATABASE_NAME
• DATABASE_USER
• DATABASE_PASSWORD
• DATABASE_HOST

14

$ python manage.py syncdb
Creating table auth_permission
Creating table auth_group
Creating table auth_user
Creating table auth_message
Creating table django_content_type
Creating table django_session
Creating table django_site

You just installed Django's auth system,
which means you don't have any superusers defined.
Would you like to create one now? (yes/no): yes
Username (Leave blank to use 'jacob'): jacob
E-‐mail address: jacob@jacobian.org
Password:
Password (again):
Superuser created successfully.
Installing index for auth.Permission model
Installing index for auth.Message model

15

Documentation
http://django.me/about-settings
http://django.me/settings
http://django.me/manage.py

16

Exercise:
“it worked!”

17

Django Training

Part 2: Apps, models, and the admin

What’s a model?

4

MVC?
(Model-View-Controller)

5

CREATE TABLE "entries_entry" (
"id" integer NOT NULL PRIMARY KEY,
"author_id" integer NOT NULL,
"pub_date" datetime NOT NULL,
"headline" varchar(200) NOT NULL,
"slug" varchar(50) NOT NULL UNIQUE,
"summary" text NOT NULL,
"body" text NOT NULL
)

6

Scary Quirky Language

• SQL is tough
• SQL knows no version control
• DRY
• Python is fun!

7

import datetime
from django.db import models
from yabl.authors.models import Author

class Entry(models.Model):
author = models.ForeignKey(Author, related_name='entries')
pub_date = models.DateTimeField(default=datetime.datetime.now)
headline = models.CharField(max_length=200)
slug = models.SlugField(unique=True)
summary = models.TextField()
body = models.TextField()

8

$ python manage.py startapp authors

10

authors/
__init__.py
models.py
tests.py
views.py

11

INSTALLED_APPS = (
"django.contrib.auth",
"django.contrib.contenttypes",
"django.contrib.sessions",
"django.contrib.sites",
"yabl.authors",
)

12

from django.db import models

class Author(models.Model):
first_name = models.CharField(max_length=200)
last_name = models.CharField(max_length=200)
bio = models.TextField(blank=True)

13

$ python manage.py validate
0 errors found.

14

$ python manage.py sqlall authors
BEGIN;
CREATE TABLE "authors_author" (
"id" integer NOT NULL PRIMARY KEY,
"first_name" varchar(200) NOT NULL,
"last_name" varchar(200) NOT NULL,
"bio" text NOT NULL
);
COMMIT;

15

Creating table authors_author
Installing index for authors.Author model

16

$ python manage.py shell

[1] >>> from yabl.authors.models import Author

[2] >>> a = Author(first_name="John", last_name="Barth")

[3] >>> a.save()

17

[4] >>> Author.objects.all()
[4] : [<Author: Author object>]

[5] >>> Author.objects.create(first_name='Miguel', last_name='de Cervantes')
[5] : <Author: Author object>

[6] : [<Author: Author object>, <Author: Author object>]

[7] >>> al = Author.objects.filter(first_name='John')

[8] >>> al[0].last_name
[8] : u'Barth'

[9] >>> Author.objects.get(last_name__startswith='de').first_name
[9] : u'Miguel'

18

first_name = models.CharField(max_length=200)
last_name = models.CharField(max_length=200)
bio = models.TextField(blank=True)

def __unicode__(self):
return '%s %s' % (self.first_name, self.last_name)

20

…

class Meta:
verbose_name_plural = 'authors'
ordering = ['last_name', 'first_name']

21

[1] >>> from yabl.authors.models import Author

[2] : [<Author: John Barth>, <Author: Miguel de Cervantes>]

[3] >>> Author.objects.order_by('-‐first_name')
[3] : [<Author: Miguel de Cervantes>, <Author: John Barth>]

22

Documentation
http://django.me/models
http://www.djangobook.com/en/2.0/chapter05/

23

Exercise:
Write some apps and some models:

• Author (authors app) • Entry (entries app)
• ﬁrst_name (CharField) • author (ForeignKey)
• last_name (CharField) • pub_date (DateTimeField)
• bio (TextField) • is_published (BooleanField)
• headline (CharField)
• slug (SlugField)
• summary (TextField)
• body (TextField)

24

Django’s
admin interface

25

“ A Web-based interface,
limited to trusted site
administrators, that enables
the adding, editing and

”
deletion of site content.

— The Django Book
http://djangobook.com/en/2.0/chapter06/

26

from django.contrib import admin

admin.site.register(Author)

27

INSTALLED_APPS = (
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.sites',
'django.contrib.admin',
'yabl.authors',
'yabl.entries',
)

28

Creating table django_admin_log
Installing index for admin.LogEntry model

29

from django.conf.urls.defaults import *

# Uncomment the next two lines to enable the admin:
admin.autodiscover()

urlpatterns = patterns('',
# Example:
# (r'^yabl/', include('yabl.foo.urls')),

# Uncomment the admin/doc line below and add 'django.contrib.admindocs'
# to INSTALLED_APPS to enable admin documentation:
# (r'^admin/doc/', include('django.contrib.admindocs.urls')),

# Uncomment the next line to enable the admin:
(r'^admin/', include(admin.site.urls)),
)

30


class AuthorAdmin(admin.ModelAdmin):
pass

admin.site.register(Author, AuthorAdmin)

35

Documentation
http://django.me/admin

36

Django Training

Part 3: URLs, views, and templates

page.php

script.cgi?pageid=144

StoryPage.aspx
6

0,2097,1-1-30-72-407-4752,00.html

7

/authors/
/authors/jacob/
/authors/adrian/

8

ROOT_URLCONF = "yabl.urls"

9

yabl/urls.py



(r'^authors/$', 'yabl.authors.views.author_list'),
(r'^authors/(d+)/$', 'yabl.authors.views.author_detail'),
)

10

yabl/authors/urls.py


(r'^$', 'yabl.authors.views.author_list'),
(r'^(d+)/$', 'yabl.authors.views.author_detail'),
)

11

yabl/urls.py



(r'^authors/', include('yabl.authors.urls')),
)

12

Regex crash course
a The letter “a”.
a+ One or more “a”s.
b? Zero or one “b”s.
c{1,3} One, two, or three “c”s.
. Any single character.
[abc] Either an “a”, “b”, or “c”.
[A-‐Z] Any character between “A” and “Z”.
[A-‐Za-‐z0-‐9]? Zero or one letters “A-Z”, “a-z”, or “0-9”.
(d{3,4}) A group containing three or four digits.
(w*) A group containing zero or more word characters (letters/digits).
[^/]+ One or more characters until (and not including) a forward slash.
^(joe|bob) A string starting with “joe” or “bob”.
(?P<id>d+) A group named “id” containing one or more digits.
article/$ A string ending with “article/”

13

Dissecting a request
• GET /authors/1/
• ROOT_URLCONF
• yabl.urls
• (r'^authors/', include('yabl.authors.urls'))
• yabl.authors.urls
• (r'^$', 'author_list') (no match)
• (r'^(d+)/', 'author_detail') (match!)
• author_detail(request, '1')
14

Documentation
http://django.me/urls

15

yabl/authors/views.py

from django.http import HttpResponse

def author_list(request):
return HttpResponse("This is the author list!")

17



r = "<ul>"
for a in Author.objects.all():
r += "<li>%s</li>" % a.name
r += "</ul>"
return HttpResponse(r)

18


from django import template

as = Author.objects.all()
tmpl = template.loader.get_template("authors/index.html")
context = template.Context({"authors": as})
return HttpResponse(tmpl.render(context))

19


from django.shortcuts import render

context = {"authors" : Author.objects.all()}
return render(request, "authors/index.html", context)

20


from django.http import Http404
from django.shortcuts import render_to_response

def author_detail(request, author_id):
try:
author = Author.objects.get(id=author_id)
except Author.DoesNotExist:
raise Http404()

return render(request, "authors/detail.html", {"author" : author})

21


from django.shortcuts import render_to_response, get_object_or_404

def author_detail(request, author_id):
author = get_object_or_404(Author, id=author_id)
return render(request, "authors/detail.html", {"author" : author})

22

What’s a template?

24

<!DOCTYPE HTML PUBLIC "-‐//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head><title>Authors</title></head>
<body>
<h1>Authors ({{ authors|length }} total)</h1>
<ul>
{% for a in authors %}
<li>
<a href="{{ a.id }}/">{{ a.name }}</a>
</li>
{% endfor %}
</ul>
</body>
</html>

25

Where to templates go?

• In an app’s templates directory.
• In directories speciﬁed by
settings.TEMPLATE_DIRS.
• ...

26

TEMPLATE_DIRS = [
'/path/to/some/templates/',
'/path/to/some/more/other/templates/',
]

27

TEMPLATE_DIRS = [
'/Users/jacob/Projects/stl-‐django/yabl/templates/',
]

28

<html lang="en">
<body>
<ul>
<li>
<a href="{{ a.id }}/">{{ a.name }}</a>
</li>
{% endfor %}
</ul>
</body>
</html>

29

The magic dot

• a["name"]
• a.name
• a.name()

30

<html lang="en">
<body>
<ul>
<li>
<a href="{{ a.id }}/">{{ a.name }}</a>
</li>
{% endfor %}
</ul>
</body>
</html>

31

{{ text|escape|linkbreaks }}

32

{{ text|truncatewords:"30" }}

33

<html lang="en">
<body>
<ul>
<li>
<a href="{{ a.id }}/">{{ a.name }}</a>
</li>
{% endfor %}
</ul>
</body>
</html>

34

Template inheritance

35

<html lang="en">
<head>
<title>
{% block title %}YABL{% endblock %}
</title>
</head>
<body>
<div id="content">
{% block content %}{% endblock %}
</div>
<div id="footer">
{% block footer %}Copyright blah..{% endblock %}
</div>
</body>
</html>

36

<html lang="en">
<head>
<title>
{% block title %}YABL{% endblock %}
</title>
</head>
<body>
<div id="content">
{% block content %}{% endblock %}
</div>
<div id="footer">
{% block footer %}Copyright blah..{% endblock %}
</div>
</body>
</html>

37

{% extends "base.html" %}

{% block title %}
Authors | {{ block.super }}
{% endblock %}

{% block content %}
<ul>
<li>
<a href="{{ a.id }}/">{{ a.name }}</a>
</li>
{% endfor %}
</ul>
{% endblock %}

38

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93&45;
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93$,(;
##9&0&5$;
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##!!#)$1&07'2&0&5$#66
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##ABC7/5(2174
####!"#+5718#&0&5$#"6!"#$'(+5718#"6
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##!"#$'(=7/#"6 ##9<D5;
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!"#$'(+5718#"6 !"#$'(+5718#"6
9<+7(>;
section_index.html base_generic.html 9<3&45; base.html

#

39

Inheritance tips
• {% extends %} must be the ﬁrst thing in
your template.
• More {% block %}s are better.
• If you’re duplicating content, you’re
missing a block.
• {{ block.super }}

41

Documentation
http://django.me/templates

42

Exercise:
/authors/
/authors/{id}/

/entries/
/entries/{slug}/

43

Django training

BONUS: Models and queries

Models
a.k.a. “DDL”

3

Managers
a.k.a. “table”

4

QuerySets
a.k.a. “selection”

5

Model instances
a.k.a. “row”

6

!!!"!"#$#%&'()*+,-./'"*012'.(31"456,21"7.8$9(6.:
!!!"!"
#$%&'()*"+,&"-.'/0"123!4"$%&'()*"523"-.'/0"6,&!7

!!!".#$#!";<=
!!!".
$%&'()*"+,&"-.'/0"123!

Model Manager QuerySet Instance

7

Instance methods

…

def is_by_jacob(self):
return "jacob" in self.author.name.lower()

…

[1] >>> e = Entry.objects.get(pk=1)

[2] >>> e.is_by_jacob()
[2] : False

9

“Special” instance methods

10

__unicode__

…

def __unicode__(self):
return self.headline

…

[1] >>> Entry.objects.all()
[1] : [<Entry: Man bites dog>, <Entry: Dog bites man>]

11

save

…

def save(self, **kwargs):
self.word_count = count_words(self.body)
super(Entry, self).save(**kwargs)

12

save

…

def save(self, **kwargs):
self.word_count = count_words(self.body)
super(Entry, self).save(**kwargs)

Don’t forget this part!

13

delete

…

def delete(self):
nobody = Author.objects.get(first_name='<NOBODY>')
self.entries.update(author=nobody)
super(Author, self).delete()

14

Default manager

…

objects = models.Manager()

…

[1] >>> from yabl.entries.models import Entry

[2] >>> Entry.objects
[2] : <django.db.models.manager.Manager object at 0x7eca70>

16

Custom managers

class EntryManager(models.Manager):
def future(self):
…
def past(self):
…

…

objects = EntryManager()

17

[1] >>> from yabl.entries.models import Entry

[2] >>> Entry.objects.future()
[2] : [<Entry: Hi>]

[3] >>> Entry.objects.past()

18

Documentation
http://django.me/managers

19

Filters

[1] >>> Author.objects.filter(first_name='Jacob')
[1] : [<Author: Jacob Kaplan-‐Moss>]

[2] >>> Author.objects.filter(last_name__contains='s')
[2] : [<Author: Miguel de Cervantes>, <Author: Jacob Kaplan-‐Moss>]

[3] >>> Author.objects.filter(last_name__contains='s', first_name='Miguel')
[3] : [<Author: Miguel de Cervantes>]

[4] >>> Author.objects.filter(last_name__contains='s').filter(first_name='Miguel')
[4] : [<Author: Miguel de Cervantes>]

21

Field lookups
exact, iexact name__exact='Joe'
contains, icontains name__icontains='s'

startswith, endswith,
name__endswith='nd'
istartswith, iendswith

name__in=('Joe', 'Jane')
in
author__in=Author.objects.filter(…)

gt, gte, lt, lte cost__gt=100

cost__range=(100, 500)
range
date__range=(now, tomrrow)

date__year=2009
year, month, day, week_day
date__month=7

isnull author__isnull=True
regex, iregex name__regex='^J.*b$'

22

Following relationships

[1] >>> Entry.objects.filter(author__first_name__startswith='J')
[1] : [<Entry: Hi>]

[2] >>> Author.objects.filter(entries__headline='Hi')
[2] : [<Author: Jacob Kaplan-‐Moss>]

Where’d that come from?

23

related_name

author = models.ForeignKey(Author, related_name='entries')

24

select_related()
[1] >>> e = Entry.objects.get(pk=1)

[2] >>> e.author
[2] : <Author: Jacob Kaplan-‐Moss>

Oops, that did a second, needless query.

[3] >>> e = Entry.objects.select_related().get(pk=1)

[4] >>> e.author
[5] : <Author: Jacob Kaplan-‐Moss>

No second query needed for e.author

25

Limiting select_related()

[1] >>> Entry.objects.select_related('author', 'category')

[2] >>> Entry.objects.select_related(depth=2)

26

QuerySet details

27

QuerySets are chainable

[1] >>> Entry.objects.filter(
....: headline__contains='bites',
....: ).exclude(
....: pub_date__year=2008
....: ).filter(
....: pub_date__month=9
....: )

28

QuerySets are unique

[1] >>> qs1 = Entry.objects.filter(headline__icontains='dog')

[2] >>> qs2 = qs1.exclude(pub_date__year=2008)

[3] >>> qs3 = qs1.filter(pub_date__year=2008)

29

QuerySets are lazy

[1] >>> qs = Entry.objects.filter(headline__icontains='dog')

[2] >>> qs = qs.exclude(pub_date__year=2008)

[3] >>> qs = qs.filter(author__first_name='Jacob')

[4] >>> qs

30

When QuerySets are evaluated

• Iteration for i in qs

• Slicing qs[0:5]

• Printing print qs, str(qs)

• len() len(qs)

• list() list(qs)

31

Chainable methods
filter(), exclude() qs.filter(name='Joe')

order_by() qs.order_by('-‐first_name')

reverse() qs.reverse()

distinct() qs.distinct()

values(), values_list() qs.values('first_name', 'last_name')

qs.dates('pub_date', 'year')
dates()
qs.dates('pub_date', 'month')

select_related() qs.select_related()

qs.defer('body')
defer(), only()
qs.only('body', 'headline')

qs.all()
none(), all()
qs.none()

32

Other QuerySet methods
get() e = Entry.objects.get(…)

create() e = Entry.objects.create(…)

get_or_create() e, created = Entry.objects.get_or_create(…)

count() Entry.objects.count()

in_bulk() Entry.objects.in_bulk([1, 2, 3])

latest() Entry.objects.latest('pub_date')

33

Raw SQL

[1] >>> query = "SELECT * FROM authors_author WHERE first_name = %s"

[2] >>> params = ["Jacob"]

[3] >>> Entry.objects.raw(query, params)
[3] [<Person: Jacob Kaplan-‐Moss>]

34

Entry.objects.raw(query % params)

No! 35

Aggregation
http://jacobian.org/r/django-aggregation

37

Transaction control
http://jacobian.org/r/django-transactions

38

Exercise:
/entries/future/
/entries/past/

39

What else?
• Forms, model forms, form sets, ...
• File storage - local and remote.
• Cookies, sessions, authn/authz.
• GeoDjango
• Built-in SQLi, XSS and CSRF protection.
• i18n and l10n support.
• Generic views,
• &c!

1

Thank you!
jacob@jacobian.org

http://lanyrd.com/sfypm

2

Introduction To Django (Strange Loop 2011)

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