Web development frameworks conceptualize various abstractions to make common web development paradigms easy to implement. These abstractions have to be "transparent" in that they enable developer to override where necessary. Django, a modern python framework provides a full stack framework and has pioneered best practices in defining these abstractions for various web application paradigms such as Authentication, Permissions, Sessions, Caching, Security from CSRF, File Storage, Form Validation, etc. The abstractions provided by django are transparent and extensible and are as such referred to in the community to be "Djangoic" The session covers these abstractions, their defaults and using some of their transparencies to achieve a few non-default common ends such as using cloud storage services like Amazon web services, Implementing LDAP authentication, Implementing caching using Memcached, database and NoSQL data stores. The biggest take away to the developer is the ability to identify and create other Djangoic solutions that are transparent abstractions by examining the ones implemented within django and developed by the community in open source applications.

1. Introduction Paradigms The Admin Interface The Django Advantage
Djangoic approach to implement common web
development paradigms
Lakshman Prasad
April 20, 2011

2. Concepts and abstractions used to represent elements of a program

3. CS is neither about computers nor is science - Abelson, SICP, MIT

4. Web Development Paradigms: Modeling common web patterns

5. Introduction Paradigms The Admin Interface The Django Advantage
Why

6. Introduction Paradigms The Admin Interface The Django Advantage
• For building database driven web applications

7. Introduction Paradigms The Admin Interface The Django Advantage
• For building database driven web applications
• Emphasis on Reuse, DRY and simplicity

8. Batteries Included

9. docs.djangoproject.com

10. Lets examine the batteries

11. Introduction Paradigms The Admin Interface The Django Advantage
About Me
• Active Djangonaut and active in Python world
• Part of a few popular open source django applications
github.com/becomingGuru.
• Co-Authored an ebook ”django-design-patterns”
• Architect and develop django applications at InMobi
• Earlier, Consulting and Development via Agiliq Solutions
• Developed several custom proprietory django applications
• twitter.com/becomingGuru http://becomingguru.com

12. Introduction Paradigms The Admin Interface The Django Advantage
A nerd, for a while

13. consulting since, until recently

14. Always been developing

15. Work at InMobi now

16. Introduction Paradigms The Admin Interface The Django Advantage
Introduction
Definition
About Me
Abstractions
Paradigms
Forms
Authentication/Caching/Sessions
Inernational/Human/Local ..ization
Generic Views
Sorting/Pagination/DataBrowse/GRID/Messages/Other
The Admin Interface
Admin
Databrowse
The Django Advantage
Users
Community
Endnotes

17. Software span a spectrum

18. Those that interact with hardware

19. The nuts and bolts

20. Those that solve a human problem ...

21. ... that are Complex Systems

22. Frameworks come in between ...

23. ... to achieve balance ...

24. ... and reduce cost of maintainance and development

25. Common Frameworks

26. Forms

27. Save form data to a table

28. Introduction Paradigms The Admin Interface The Django Advantage
Use a Model Form
>>> from d j a n g o . f o r m s import ModelForm
# C r e a t e t h e form c l a s s .
>>> c l a s s A r t i c l e F o r m ( ModelForm ) :
... c l a s s Meta :
... model = A r t i c l e
# C r e a t i n g a form t o add an a r t i c l e .
>>> form = A r t i c l e F o r m ( )
# C r e a t i n g a form t o c h an ge an e x i s t i n g a r t i c l e .
>>> a r t i c l e = A r t i c l e . o b j e c t s . g e t ( pk=1)
>>> form = A r t i c l e F o r m ( i n s t a n c e= a r t i c l e )

29. Introduction Paradigms The Admin Interface The Django Advantage
Save Foreign Keys

30. Introduction Paradigms The Admin Interface The Django Advantage
Use Model Formset
from d j a n g o . f o r m s . m o d e l s i m p o r t m o d e l f o r m s e t f a c t o r y
AuthorFormSet = m o d e l f o r m s e t f a c t o r y ( Author )
f o r m s e t = A ut h o r F o r m Se t ( )
> > print formset
>
<i n p u t t y p e=” h i d d e n ” name=” form− TOTAL FORMS”
v a l u e=” 1 ” i d=” i d f o r m − TOTAL FORMS” />
<i n p u t t y p e=” h i d d e n ” name=” form−INITIAL FORMS”
v a l u e=” 0 ” i d=” i d f o r m −INITIAL FORMS” />
<i n p u t t y p e=” h i d d e n ” name=” form− MAX NUM FORMS”
i d=” i d f o r m −MAX NUM FORMS” />
<t r > <th>
<l a b e l f o r=” i d f o r m −0 −name”>Name:</ l a b e l >
</th> <td>
<i n p u t i d=” i d f o r m −0 −name” t y p e=” t e x t ”
name=” form−0 −name” m a x l e n g t h=” 100 ” />
</td> </t r >

31. Introduction Paradigms The Admin Interface The Django Advantage
Model Formset options
f o r m s e t = AuthorFormSet ( q s=Au th o r . o b j e c t s . a l l ( ) ,
e x t r a =5)
formset . i s v a l i d ()
formset . e r r o r s
{ ’ name ’ : ’ T h i s f i e l d is required ’}
formset . changed forms
formset . save ()

32. Introduction Paradigms The Admin Interface The Django Advantage
Form pre populated

33. Introduction Paradigms The Admin Interface The Django Advantage
Forms dont have to save to a Model
from d j a n g o import f o r m s
c l a s s ContactForm ( f o r m s . Form ) :
s u b j e c t = f o r m s . C h a r F i e l d ( m a x l e n g t h =100)
message = f o r m s . C h a r F i e l d ( )
sender = forms . E m a i l F i e l d ()
c c m y s e l f = f o r m s . B o o l e a n F i e l d ( r e q u i r e d=F a l s e )
def s a v e ( s e l f ) :
#Do a n y t h i n g
...

34. Form Preview

35. Introduction Paradigms The Admin Interface The Django Advantage
Form Preview
from d j a n g o . c o n t r i b . f o r m t o o l s . p r e v i e w import FormPreview
from myapp . m o d e l s import SomeModel
#Add a u r l
( r ’ ˆ p o s t / $ ’ , SomeModelFormPreview ( SomeModelForm ) ) ,
#D e f i n e form p r e v i e w
c l a s s SomeModelFormPreview ( FormPreview ) :
def done ( s e l f , r e q u e s t , c l e a n e d d a t a ) :
# Do s o m e t h i n g w i t h t h e c l e a n e d d a t a , t h e n
# r e d i r e c t t o a ” s u c c e s s ” page .
r e t u r n H t t p R e s p o n s e R e d i r e c t ( ’ / form / s u c c e s s ’ )

36. Form Wizard

37. Introduction Paradigms The Admin Interface The Django Advantage
Form Wizard
c l a s s C o n t a c t W i z a r d ( FormWizard ) :
def done ( s e l f , r e q u e s t , f o r m l i s t ) :
do something with the form data ( fo r m l is t )
return HttpResponseRedirect ( ’ / r e d i r e c t / ’ )

38. Introduction Paradigms The Admin Interface The Django Advantage
CSRF Protection
<form a c t i o n=” ” method=” p o s t ”>{% c s r f t o k e n %}
from d j a n g o . v i e w s . d e c o r a t o r s . c s r f import c s r f p r o t e c t
from d j a n g o . t e m p l a t e import R e q u e s t C o n t e x t
@csrf protect
def my view ( r e q u e s t ) :
c = {}
# ...
r e t u r n r e n d e r t o r e s p o n s e ( ” a t e m p l a t e . html ” , c ,
c o n t e x t i n s t a n c e=
RequestContext ( request ))

39. Introduction Paradigms The Admin Interface The Django Advantage
Authentication: Point to url pattern
u r l p a t t e r n s += p a t t e r n s ( ’ d j a n g o . c o n t r i b . a u t h . v i e w s ’ ,
u r l ( r ’ ˆ l o g i n /$ ’ , ’ l o g i n ’ ) ,
u r l ( r ’ ˆ l o g o u t /$ ’ , ’ l o g o u t ’ ) ,
u r l ( r ’ ˆ r e g i s t e r /$ ’ , ’ r e g i s t e r ’ ) ,
u r l ( r ’ ˆ p a s s r e s e t /$ ’ , ’ p a s s w o r d r e s e t ’ ) ,
u r l ( r ’ ˆ p a s s r e s e t 2 /$ ’ , ’ p a s s w o r d r e s e t d o n e ’ ) ,
u r l ( r ’ ˆ p a s s r e s e t c o n f i r m / ( ?P<u i d b 3 6 >[−w]+)/ ’ ,
’ password reset confirm ’ ) ,
u r l ( r ’ ˆ p a s s r e s e t c o m p l e t e /$ ’ ,
’ password reset complete ’ ) ,
)

40. Introduction Paradigms The Admin Interface The Django Advantage
Login Required
from d j a n g o . c o n t r i b . a u t h . d e c o r a t o r s import
login required
@ l o g i n r e q u i r e d ( r e d i r e c t f i e l d n a m e= ’ r e d i r e c t t o ’ )
def my view ( r e q u e s t ) :
...

41. Introduction Paradigms The Admin Interface The Django Advantage
Authentication backends
class SettingsBackend :
”””
A u t h e n t i c a t e a g a i n s t t h e s e t t i n g s ADMIN LOGIN
and ADMIN PASSWORD .
”””
def a u t h e n t i c a t e ( s e l f , username=None , p a s s w o r d=None )
i f l o g i n v a l i d and p w d v a l i d :
return user
r e t u r n None
def g e t u s e r ( s e l f , u s e r i d ) :
try :
r e t u r n U s e r . o b j e c t s . g e t ( pk=u s e r i d )
except U s e r . D o e s N o t E x i s t :
r e t u r n None

42. django-socialauth

43. Introduction Paradigms The Admin Interface The Django Advantage
Open ID backend
c l a s s OpenIdBackend :
d e f a u t h e n t i c a t e ( s e l f , o p e n i d k e y , r e q u e s t , p r o v i d e r , u s e r=None ) :
try :
a s s o c = U s e r A s s o c i a t i o n . o b j e c t s . g e t ( o p e n i d k e y=o p e n i d k e y )
return assoc . user
except U s e r A s s o c i a t i o n . DoesNotExist :
#f e t c h i f o p e n i d p r o v i d e r p r o v i d e s any s i m p l e r e g i s t r a t i o n f i e l d s
i f r e q u e s t . o p e n i d and r e q u e s t . o p e n i d . s r e g :
email = request . openid . sreg . get ( ’ email ’ )
nickname = r e q u e s t . openid . s r e g . get ( ’ nickname ’ )
firstname , lastname = ( request . openid . sreg
. get ( ’ fullname ’ , ’ ’ )
return user
d e f GooglesAX ( s e l f , o p e n i d r e s p o n s e ) :
e m a i l = ( o p e n i d r e s p o n s e . ax
. g e t S i n g l e ( ’ h t t p : / / axschema . o r g / c o n t a c t / e m a i l ’ ) )
f i r s t n a m e = ( o p e n i d r e s p o n s e . ax
. g e t S i n g l e ( ’ h t t p : / / axschema . o r g / namePerson / f i r s t ’ ) )
l a s t n a m e = ( o p e n i d r e s p o n s e . ax
. g e t S i n g l e ( ’ h t t p : / / axschema . o r g / namePerson / l a s t ’ ) )
return l o c a l s ()
def g e t u s e r ( s e l f , u s e r i d ) :
try :
u s e r = U s e r . o b j e c t s . g e t ( pk=u s e r i d )
return user
except User . DoesNotExist :
r e t u r n None

44. ”Normalized data is for sissies” - Cal Henderson

45. Introduction Paradigms The Admin Interface The Django Advantage
Different blocks need different caching durations

46. Introduction Paradigms The Admin Interface The Django Advantage
Generally Memcache Every page
CACHE BACKEND = ’ memcached : / / 1 2 7 . 0 . 0 . 1 : 1 1 2 1 1 / ’
CACHE BACKEND = ’ memcached : / / 1 7 2 . 1 9 . 2 6 . 2 4 0 : 1 1 2 1 1 ;
172.19.26.242:11212;172.19.26.244:11213/ ’

47. Introduction Paradigms The Admin Interface The Django Advantage
Implement a caching decorator
from d j a n g o . c o r e . c a c h e import c a c h e
def c a c h e f o r ( s e c o n d s , f e t c h =0):
def c a c h e i t ( f u n c ) :
def d e c o f u n c ( s e l f ) :
v a l = cache . get ( s e l f . g e t c a c h e k e y ( f e t c h ))
i f not v a l :
val = func ( s e l f )
cache . s e t ( s e l f . g e t c a c h e k e y ( f e t c h ) ,
val , seconds )
return v a l
return deco func
return c a c h e i t

48. Introduction Paradigms The Admin Interface The Django Advantage
Apply on the blocks
class TwitterBlock ( TwitterSearchBlock ) :
t e m p l a t e n a m e = ’ t w i t t e r u s e r b l o c k . html ’
a j a x t e m p l a t e = ’ t w e e t s u s e r . html ’
@ c a c h e f o r ( 6 0 ∗ 6 0 , f e t c h =1)
def f e t c h d a t a ( s e l f ) :
tw = T w i t t e r ( e m a i l= ’ umoja com ’ )
u s e r t w e e t s = tw . s t a t u s e s . u s e r t i m e l i n e (
s c r e e n n a m e= s e l f . d a t a )
r e t u r n u s e r t w e e t s , None

49. Introduction Paradigms The Admin Interface The Django Advantage
Different cache Backends
• Database
• File System
• Local Memory
• Redis, a NoSQL store
• Dummy- For Development
• Sessions can use any of these, or the database.

50. Introduction Paradigms The Admin Interface The Django Advantage
Humanization and Localization
19 Apr 2 0 1 0 | n a t u r a l d a y becomes ‘ y e s t e r d a y ‘ .
20 Apr 2 0 1 0 | n a t u r a l d a y becomes ‘ today ‘ .
1 | o r d i n a l becomes ‘ 1 s t ‘ .
2 | o r d i n a l becomes ‘ 2 nd ‘ .
1 0 0 0 0 0 0 | i n t w o r d becomes ‘ 1 . 0 m i l l i o n ‘ .
1 2 0 0 0 0 0 | i n t w o r d becomes ‘ 1 . 2 m i l l i o n ‘ .
{{ v a l u e | l o c a l i z e }}

51. Introduction Paradigms The Admin Interface The Django Advantage
Internationalization
{% b l o c k t r a n s w i t h amount= a r t i c l e . p r i c e %}
That w i l l c o s t $ {{ amount } } .
{% e n d b l o c k t r a n s %}
{% b l o c k t r a n s w i t h myvar=v a l u e | f i l t e r %}
T h i s w i l l ha ve {{ myvar }} i n s i d e .
{% e n d b l o c k t r a n s %}
c l a s s in . forms . I N S t a t e F i e l d
c l a s s in . forms . INZipCodeField
c l a s s in . forms . I N S t a t e S e l e c t

52. Introduction Paradigms The Admin Interface The Django Advantage
Using Generic Views
# some app / v i e w s . py
from d j a n g o . v i e w s . g e n e r i c import TemplateView
c l a s s AboutView ( TemplateView ) :
t e m p l a t e n a m e = ” a b o u t . html ”
# u r l s . py
from d j a n g o . c o n f . u r l s . d e f a u l t s import ∗
from some app . v i e w s import AboutView
urlpatterns = patterns ( ’ ’ ,
( r ’ ˆ a b o u t / ’ , AboutView . a s v i e w ( ) ) ,
)

53. Introduction Paradigms The Admin Interface The Django Advantage
List and Object Views
from d j a n g o . v i e w s . g e n e r i c import L i s t V i e w
from b o o k s . m o d e l s import Book
c l a s s AcmeBookListView ( L i s t V i e w ) :
context object name = ” book list ”
q u e r y s e t = Book . o b j e c t s . f i l t e r ( p u b l i s h e r n a m e=
”Acme P u b l i s h i n g ” )
t e m p l a t e n a m e = ” b o o k s / a c m e l i s t . html ”

54. Introduction Paradigms The Admin Interface The Django Advantage
Mixins
from d j a n g o i m p o r t h t t p
from d j a n g o . u t i l s i m p o r t s i m p l e j s o n a s j s o n
c l a s s JSONResponseMixin ( o b j e c t ) :
def r e n d e r t o r e s p o n s e ( s e l f , context ) :
” R e t u r n s a JSON r e s p o n s e c o n t a i n i n g ’ c o n t e x t ’ a s p a y l o a d ”
return s e l f . get json response ( s e l f . convert context to json ( context ))
d e f g e t j s o n r e s p o n s e ( s e l f , c o n t e n t , ∗∗ h t t p r e s p o n s e k w a r g s ) :
” C o n s t r u c t an ‘ H t t p R e s p o n s e ‘ o b j e c t . ”
return http . HttpResponse ( content ,
c o n t e n t t y p e= ’ a p p l i c a t i o n / j s o n ’ ,
∗∗ h t t p r e s p o n s e k w a r g s )
def c o n v e r t c o n t e x t t o j s o n ( s e l f , context ) :
” C o n v e r t t h e c o n t e x t d i c t i o n a r y i n t o a JSON o b j e c t ”
r e t u r n j s o n . dumps ( c o n t e x t )

55. Introduction Paradigms The Admin Interface The Django Advantage
Any combinations of Mixins
c l a s s H y b r i d D e t a i l V i e w ( JSONResponseMixin ,
SingleObjectTemplateResponseMixin ,
BaseDetailView ) :
def r e n d e r t o r e s p o n s e ( s e l f , context ) :
# Look f o r a ’ f o r m a t=j s o n ’ GET argument
i f s e l f . r e q u e s t . GET . g e t ( ’ f o r m a t ’ , ’ h t m l ’ ) == ’ j s o n ’ :
r e t u r n JSONResponseMixin . r e n d e r t o r e s p o n s e ( s e l f , c o n t e x t )
else :
return SingleObjectTemplateResponseMixin . render to response ( s e l f ,
context )

56. Introduction Paradigms The Admin Interface The Django Advantage
Types of Generic Views
• Simple: Redirect, Render to Template
• Detail, List View
• Archive View: Date, Month, Year views
• Basic CRUD, with or w/o Auth

57. Introduction Paradigms The Admin Interface The Django Advantage
Builtin support for Pagination
>>> from d j a n g o . c o r e . p a g i n a t o r import P a g i n a t o r
>>> o b j e c t s = [ ’ j o h n ’ , ’ p a u l ’ , ’ g e o r g e ’ , ’ r i n g o ’ ]
>>> p = P a g i n a t o r ( o b j e c t s , 2 )
>>> p . count
4
>>> p . num pages
2
>>> p . page range
[1 , 2]
>>> page1 = p . page ( 1 )
>>> page1
<Page 1 o f 2>
>>> page1 . o b j e c t l i s t
[ ’ john ’ , ’ paul ’ ]

58. Introduction Paradigms The Admin Interface The Django Advantage
Abstract the pagination in middleware
django pagenation
{% a u t o p a g i n a t e o b j e c t l i s t 10 %}
{% p a g i n a t e %}

59. DataGrid enables user customisable column and sorting

60. Introduction Paradigms The Admin Interface The Django Advantage
Other common paradigms
• Display Image Thumbnail
• Store data on a CDN, like Amazon S3
• Periodic tasks with Celery
• Decoupled design using Signals
• GeoDjango : Framework for all location based applications

62. Introduction Paradigms The Admin Interface The Django Advantage
Admin by models alone

63. Introduction Paradigms The Admin Interface The Django Advantage
Admin Syntax
from d j a n g o . c o n t r i b import admin
from m o d e l s import Post , Comment
c l a s s PostAdmin ( admin . ModelAdmin ) :
l i s t d i s p l a y = ( ’ t i t l e ’ , ’ datetime ’ )
c l a s s CommentAdmin ( admin . ModelAdmin ) :
l i s t d i s p l a y = ( ’ text ’ ,)
admin . s i t e . r e g i s t e r ( Post , PostAdmin )
admin . s i t e . r e g i s t e r ( Comment , CommentAdmin )

64. List Page

65. Add an Entry

66. Auto Validation

67. Introduction Paradigms The Admin Interface The Django Advantage
Databrowse enables browsable web complete with
hyperlinks

68. Introduction Paradigms The Admin Interface The Django Advantage
Popular Users
• Media
• LA Times
• NY Times
• Washington Post
• Guardian
• Hindustan TImes

69. Introduction Paradigms The Admin Interface The Django Advantage
Popular Users
• Media
• LA Times
• NY Times
• Washington Post
• Guardian
• Hindustan TImes
• Web2.0
• Mahalo: 10 million Page views
• Many web startups: Convore, Lanyard, Everyblock,
GroupQuality,

70. Django users

71. Introduction Paradigms The Admin Interface The Django Advantage
NASA uses Django
After an extensive trade study, we selected Django ...
as the first and primary application environment for the
Nebula Cloud.

72. 700 contibutors

73. More open source projects than you think ...

74. ... one for every size and style

75. Don’t go where the puck is; go where the puck is going to be

77. Introduction Paradigms The Admin Interface The Django Advantage
Image Attributions
h t t p : / /www . f l i c k r . com/ p h o t o s / t e j e d o r o d e l u z /3157690060/
h t t p : / /www . f l i c k r . com/ p h o t o s /23820645 @N05 /4287681570/
h t t p : / /www . f l i c k r . com/ p h o t o s / a i d a n j o n e s /3575000735/
http :// j a c o b i a n . org /
h t t p : / / s a n j u a n c o l l e g e . edu / l i b / i m a g e s / p h i l o s o p h y b r a i n . j p g
h t t p : / /www . f l i c k r . com/ p h o t o s / uhop /105062059/
h t t p : / / s 3 . amazonaws . com/memebox/ u p l o a d s /136/ e x p o n e n t i a l g r a p h 2 . j p g
h t t p : / / g e e k a n d p o k e . t y p e p a d . com/ g e e k a n d p o k e / i m a g e s /2008/06/03/ s e x p l 1 8 . j p g
h t t p : / /www . f l i c k r . com/ p h o t o s / go /253819/
h t t p : / / a r o u n d t h e s p h e r e . f i l e s . w o r d p r e s s . com /2009/05/ s w i s s −army−k n i f e . j p g
h t t p : / /www . f r e e f o t o . com/ i m a g e s /41/04/41 0 4 9− −Keep−L e f t w e b . j p g
−
h t t p : / /www . f l i c k r . com/ p h o t o s / o r i n r o b e r t j o h n /114430223/

78. hello@lakshmanprasad.com