In the early days, Web developers wrote every page by hand. Updating a Web site meant editing HTML; a "redesign" involved redoing every single page, one at a time.
As Web sites grew and became more ambitious, it quickly became obvious that that situation was tedious, time-consuming, and ultimately untenable. A group of enterprising hackers at NCSA (the National Center for Supercomputing Applications, where Mosaic, the first graphical Web browser, was developed) solved this problem by letting the Web server spawn external programs that could dynamically generate HTML. They called this protocol the Common Gateway Interface, or CGI, and it changed the Web forever.
It's hard now to imagine what a revelation CGI must have been: instead of treating HTML pages as simple files on disk, CGI allows you to think of your pages as resources generated dynamically on demand. The development of CGI ushered in the first generation of dynamic Web sites.
However, CGI has its problems: CGI scripts need to contain a lot of repetitive "boilerplate" code, they make code reuse difficult, and they can be difficult for first-time developers to write and understand.
PHP fixed many of these problems, and it took the world by storm -- it's now by far the most popular tool used to create dynamic Web sites, and dozens of similar languages and environments (ASP, JSP, etc.) followed PHP's design closely. PHP's major innovation is its ease of use: PHP code is simply embedded into plain HTML; the learning curve for someone who already knows HTML is extremely shallow.
But PHP has its own problems; its very ease of use encourages sloppy, repetitive, ill-conceived code. Worse, PHP does little to protect programmers from security vulnerabilities, and thus many PHP developers found themselves learning about security only once it was too late.
These and similar frustrations led directly to the development of the current crop of "third-generation" Web development frameworks. These frameworks -- Django and Ruby on Rails appear to be the most popular these days -- recognize that the Web's importance has escalated of late. With this new explosion of Web development comes yet another increase in ambition; Web developers are expected to do more and more every day.
Django was invented to meet these new ambitions. Django lets you build deep, dynamic, interesting sites in an extremely short time. Django is designed to let you focus on the fun, interesting parts of your job while easing the pain of the repetitive bits. In doing so, it provides high-level abstractions of common Web development patterns, shortcuts for frequent programming tasks, and clear conventions on how to solve problems. At the same time, Django tries to stay out of your way, letting you work outside the scope of the framework as needed. We wrote this book because we firmly believe that Django makes Web development better. It's designed to quickly get you moving on your own Django projects, and then ultimately teach you everything you need to know to successfully design, develop, and deploy a site that you'll be proud of.
We're extremely interested in your feedback. The online version of this book will let you comment on any part of the book, and discuss it with other readers. We'll do our best to read all the comments posted there, and to respond to as many as possible. If you prefer email, please drop us a line at email@example.com. Either way, we'd love to hear from you! We're glad you're here, and we hope you find Django as exciting, fun, and useful as we do.