1. Python Meta classes and how
Django uses them Lakshman Prasad

2. Meta Classes
 A Design pattern
 Dynamically create classes
 Enables Flexibility, Good API
 Used by Frameworks
 Perform “Magic”

3. Where Meta Classes?
 Frameworks, frameworks, frameworks.
 Django uses them extensively.
 Scrappy, a web scrapping framework.
 Flexible Django apps. Eg: Django-registration

5. Executes the code when encountered
Creates namespace and stores all variables in it

6. `type` is an inbuilt MetaClass
Dynamic class = Static classes

7. `__metaclass__` defines metaclases

8. Meta Class Magic
Define a class extending object
Examined type is string, Magic!
Enables Declarative Syntax

9. MetaClasses, not always
 Simple function decorators
 Unintuitive to end developers, unless
explained
 Python 2.6+ has Class Decorators
 But being powerful, where they are needed,
indespesible

10. Django Models

11. Django Models Creation
 Declarative Syntax, No `__metaclass__`
 New model created in place
 Options into `Options` object
 Register in registry called `AppCache`
 Add attributes to new model

12. Inside Django Models
 Return the same registered Model from
AppCache
 Original options and Meta options stored in
`_meta`
 Add more useful attributes/classes like
`DoesnotExist`, `module_name` and
`class_name`

13. Django Forms

14.  Rendering in html
 Validation for right data
 Displaying errors
 Customization options
 Provided model, storing to the database

15. Dynamic Django forms - 1
Forms API is flexible, but often needs Meta Classes
`base_fields` and `fields` list store all fields
Change field attributes while initialization

16. Dynamic Django Forms - 2
When high complexity, instantiate a form,
dynamically

17. Resources
Python, Django Documentation, Source.
Pro Django, by Marty Alchin
Django-registration v0.7 by James Bennett

18. Thank You!
lakshman@uswaretech.com
: Build Cutting Edge Web Apps.
Small Team of expert Django Developers.
Exclusively develop in Django, Python stack.
@becomingGuru, @uswaretech