Django: The Good Parts

James Bennett (Release Manager for Django)

• July 2005: Initial public preview
• Now: 160 kLOC of Python in Django 1.7

Aren't other frameworks smaller/lighter and thus better?

The Good Parts

• HTTP abstraction + request/response cycle
• Conservative (really!) approach to features
• The secret weapons: apps

HTTP Abstraction

HTTP sucks

• Nine different request methods with big differences
• Unicode-unaware
• Persistence, auth ,streaming, security al tacked on/afterthoughts

CGI isn't great, either

• How to CGI
  • Write script to be invoked by web server; request information will be in environment variables
  • submitted data received via standar input
  • script does it processing
• How CGI is actually done
  • Script maybe invoked by web server
  • chmod 777 everything
  • environment is full of LIES
  • give up figuring out what the actual request URL was

WSGI is basically CGI with a bit of Python

• Having a standard is good, but...
  • It's CGI-style; you to constantly reparse environment variables
  • signaling up and down the stack requires inventing ad-hoc protocols
  • return/response API sucks
  • inherits HTTP's awful approach to character encoding

We can do better

• HttpRequest
  • already parsed and normalize for you
  • sensible attribute and dictionary-based access
  • relatively san handling of character encoding
• HttpResponse
  • easy to construct and manipulate
  • convenient sublcasses for common specialed responses (404, redirect, etc.)
• Write a callable that takes a HttpRequest and returns an HttpResponse
• Write simple URL routing

Life cycle

• Middleware system baked in... all middleware systems suck, though
• Signals!
• Decorators!
• Call other stuff - it's callables all the way down

Django does PEP 333 so you don't have to

• A Django project is a WSGI application
• wsgi.py + WSGI_APPLICATION

Sane HTTP/WSGI is worth importing some stuff

Compassionate Conservatism

Features take a while to get in

• The truncatechars function only took 4 years!
• Migrations only took 6 years!

Unbundling/removing

• contrib.comments
• contrib.databrowse
• contrib.localflavor
• contrib.markup

Things are difficult to add, easier to remove. This is usually described as a bad thing.

Conservatism

• strong preference or community solutions (e.g., Migrations: South won the migration wars)
• core framework more about providing API support
• more "swappable" components than expected (e.g., Jinja2 instead of the template system)
• more stability over time
• features land when ready
• competition often produces better solutions
• Django stays remarkable consistent and stable... this is good!

Enc-app-sulation

• A Django project is a WSGI application. But what is a Django application?

Django Applications

• Django apps can be...
  • models
  • views
  • forms
  • etc.
  • Not generally a black box
• Django gives you safe APIs, meaning you can make safe assumptions and safer integration
• Django applications are encapsulated, pluggable functionality
  • Key selling point of Django
  • Apps are a secret weapon
• A Django application can do one thing and do it well
• Django Packages lists 2,206 available apps