Daniel Greenfeld - Two Scoops of Django: Best Practices For Django 1.5

Two Scoops of Django: Best Practices for Django 1.5
First Edition, Final Version, 20130823
by Daniel Greenfeld and Audrey Roy

Copyright 2013 Daniel Greenfeld, Audrey Roy, and Cartwheel Web.

All rights reserved. This book may not be reproduced in any form, in whole or in part, without written permission from the authors, except in the case of brief quotations embodied in articles or reviews.

Limit of Liability and Disclaimer of Warranty: The authors have used their best efforts in preparing this book, and the information provided herein as is. The information provided is sold without warranty, either express or implied. Neither the authors nor Cartwheel Web will be held liable for any damages to be caused either directly or indirectly by the contents of this book.

Trademarks: Rather than indicating every occurrence of a trademarked name as such, this book uses the names only in an editorial fashion and to the benefit of the trademark owner with no intention of infringement of the trademark.

Third printing, August 2013

For more information, visit https://django.2scoops.org .

For Malcolm Tredinnick
1971-2013
We miss you.

• About the Mobile Edition

  Technical books are notorious for having formatting issues and poor editing whenconverted to Kindle and ePub formats. When we set out to convert Two Scoops ofDjango to flow properly in ebook readers, we knew that we wanted things to bedifferent.

  We, the authors of this book, have tried very, very hard to ensure a high-qualityreading experience in ebook readers. Specifically:

  • Some tables have been rewritten as bulleted lists for improved readability.
  • Many code samples have been edited to read better on small ebook reader screens. We manually checked every single code sample multiple times on various ebook readers, adjusting the code to flow as nicely as possible. The results are not perfect, but they are as close as we could come.
  • All code samples are displayed as text rather than images. (We actually tried converting them all to 300dpi images, but the experience of seeing actual text was better than that of seeing images and zooming in.)
  • We read the book forwards and backwards in a variety of ebook readers to make sure that the formatting looked decent.

  Presenting technical content on mobile devices presents a unique challenge, sincereformatting large-page content for small screens and testing the content acrossmultiple formats and devices is not a trivial task.

  We decided early on to focus on quality and presentation, and we think that ourformatting and testing efforts have been worthwhile. We hope that the resultingreading experience is pleasant and enjoyable. If you notice formatting issues or havesuggestions about how to improve the reading experience, wed love to hear fromyou.

  Authors Notes
  A Few Words From Daniel Greenfeld

  In the spring of 2006, I was working for NASA on a project that implemented aJava-based RESTful web service that was taking weeks to deliver. One evening, whenmanagement had left for the day, I reimplemented the service in Python in 90minutes.

  I knew then that I wanted to work with Python.

  I wanted to use Django for the web front-end of the web service, but managementinsisted on using a closed-source stack because Django is only at version 0.9x, hencenot ready for real projects. I disagreed, but stayed happy with the realization thatat least the core architecture was in Python. Django used to be edgy during thoseheady days, and it scared people the same way that Node.js scares peopletoday.

  Nearly seven years later, Django is considered a mature, powerful, secure, stableframework used by incredibly successful corporations (Instagram, Pinterest,Mozilla, etc.) and government agencies (NASA, et al) all over the world.Convincing management to use Django isnt hard anymore, and if it is hard toconvince them, finding jobs which let you use Django has become mucheasier.

  In my 6+ years of building Django projects, Ive learned how to launch new webapplications with incredible speed while keeping technical debt to an absoluteminimum.

  My goal in this book is to share with you what Ive learned. My knowledge andexperience have been gathered from advice given by core developers, mistakes Ivemade, successes shared with others, and an enormous amount of note taking. Imgoing to admit that the book is opinionated, but many of the leaders in the Djangocommunity use the same or similar techniques.

  This book is for you, the developers. I hope you enjoy it!

  A Few Words From Audrey Roy

  I first discovered Python in a graduate class at MIT in 2005. In less than 4 weeks ofhomework assignments, each student built a voice-controlled system fornavigating between rooms in MITs Stata Center, running on our HP iPaqsrunning Debian. I was in awe of Python and wondered why it wasnt used foreverything. I tried building a web application with Zope but struggled withit.

  A couple of years passed, and I got drawn into the Silicon Valley tech startupscene. I wrote graphics libraries in C and desktop applications in C++ for a startup.At some point, I left that job and picked up painting and sculpture. Soon I wasdrawing and painting frantically for art shows, co-directing a 140-person art show,and managing a series of real estate renovations. I realized that I was doing a lot atonce and had to optimize. Naturally, I turned to Python and began writing scripts togenerate some of my artwork. That was when I rediscovered the joy of working withPython.

  Many friends from the Google App Engine, SuperHappyDevHouse, and hackathonscenes in Silicon Valley inspired me to get into Django. Through them and throughvarious freelance projects and partnerships I discovered how powerful Djangowas.

  Before I knew it, I was attending PyCon 2010, where I met my fiance DanielGreenfeld. We met at the end of James Bennetts Django In Depth tutorial, and nowthis chapter in our lives has come full circle with the publication of thisbook.

  Django has brought more joy to my life than I thought was possible with a webframework. My goal with this book is to give you the thoughtful guidance oncommon Django development practices that are normally left unwritten (or implied),so that you can get past common hurdles and experience the joy of using the Djangoweb framework for your projects.

  Introduction

  Our aim in writing this book is to write down all of the unwritten tips, tricks, andcommon practices that weve learned over the years while working withDjango.

  While writing, weve thought of ourselves as scribes, taking the various thingsthat people assume are common knowledge and recording them with simpleexamples.

  A Word About Our Recommendations

  Like the official Django documentation, this book covers how to do things in Django,illustrating various scenarios with code examples.

  Unlike the Django documentation, this book recommends particular coding styles,patterns, and library choices. While core Django developers may agree with some ormany of these choices, keep in mind that many of our recommendations arejust that: personal recommendations formed after years of working withDjango.

  Throughout this book, we advocate certain practices and techniques that weconsider to be the best approaches. We also express our own personal preferences forparticular tools and libraries.

  Sometimes we reject common practices that we consider to be anti-patterns. Formost things we reject, we try to be polite and respectful of the hard work of theauthors. There are the rare, few things that we may not be so polite about. This is inthe interest of helping you avoid dangerous pitfalls.