Tài liệu Python web development with django

www.it-ebooks.info Python Web Development with Django® www.it-ebooks.info Developer’s Library ESSENTIAL REFERENCES FOR PROGRAMMING PROFESSIONALS Developer’s Library books are designed to provide practicing programmers with unique, high-quality references and tutorials on the programming languages and technologies they use in their daily work. All books in the Developer’s Library are written by expert technology practitioners who are especially skilled at organizing and presenting information in a way that’s useful for other programmers. Key titles include some of the best, most widely acclaimed books within their topic areas: PHP & MySQL Web Development Python Essential Reference Luke Welling & Laura Thomson ISBN 978-0-672-32916-6 David Beazley ISBN-13: 978-0-672-32862-6 MySQL Programming in Objective-C Paul DuBois ISBN-13: 978-0-672-32938-8 Stephen G. 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The authors and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein. The publisher offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales, which may include electronic versions and/or custom covers and content particular to your business, training goals, marketing focus, and branding interests. For more information, please contact: U.S. Corporate and Government Sales (800) 382-3419 [email protected] For sales outside the United States, please contact: Editor-In-Chief Mark Taub Acquisitions Editor Debra Williams Cauley Development Editor Michael Thurston Managing Editor Kristy Hart Project Editor and Copy Editor Jovana San Nicolas-Shirley Indexer Cheryl Lenser Proofreader Geneil Breeze International Sales [email protected] Publishing Coordinator Kim Boedigheimer Visit us on the Web: informit.com/aw Library of Congress Cataloging-in-Publication Data: Forcier, Jeff, 1982Python web development with Django / Jeff Forcier, Paul Bissex, Wesley Chun. p. cm. Includes index. ISBN-10: 0-13-235613-9 (pbk. : alk. paper) ISBN-13: 978-0-13-235613-8 (pbk. : alk. paper) 1. Web site development. 2. Django (Electronic resource) 3. Python (Computer program language) 4. Web sites—Authoring programs. I. Bissex, Paul. II. Chun, Wesley. III. Title. TK5105.8885.D54F68 2009 006.7’6—dc22 2008037134 Copyright © 2009 Pearson Education, Inc. All rights reserved. Printed in the United States of America. This publication is protected by copyright, and permission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, write to: Pearson Education, Inc Rights and Contracts Department 501 Boylston Street, Suite 900 Boston, MA 02116 Fax (617) 671 3447 ISBN-13: 978-0-13-235613-8 ISBN-10: 0-13-235613-9 Text printed in the United States on recycled paper at RR Donnelley in Crawfordsville, Indiana. First printing October 2008 www.it-ebooks.info Cover Designer Gary Adair Compositor Jake McFarland ❖ To Brian Levine, for introducing me to Python, a small thing that has made a big difference.To my parents, for allowing me to monopolize the family computer while growing up. And to my wife, for her loving support and understanding. —Jeff Forcier To my late father Henry, who taught me to tinker; to my mother Glenda, who taught me to write; and to my wife Kathleen, a brilliant star in my life. —Paul Bissex To my wonderful children, Leanna Xin-Yi and Daylen Xin-Zhi, for whom I’ve had to develop multiple pairs of eyes with which to keep watch over, and who are miraculously able to temporarily transport me back in time to remind me of what childhood and its amazing wonders were like. —Wesley Chun ❖ www.it-ebooks.info Table of Contents Introduction 1 Where Web Frameworks Come From 1 A Better Way 2 We’re Not in Kansas Anymore 2 Web Development Is Better with Python and Django 3 I: Getting Started 1 Practical Python for Django Python Skills Are Django Skills Getting Started: Python’s Interactive Interpreter Python Basics 7 7 8 10 Comments 10 Variables and Assignment 10 Operators 11 Python Standard Types 11 Object Boolean Values 12 Numbers 12 Numeric Operators 13 Numeric Built-in and Factory Functions 14 Sequences and Iterables 14 Lists 17 Strings 19 Sequence Built-ins and Factory Functions 25 Mapping Type: Dictionaries 26 Standard Type Summary 28 Flow Control 28 Conditionals 29 Loops 29 Exception Handling 30 The finally Clause 31 Throwing Exceptions with raise 32 Files 33 Functions 34 www.it-ebooks.info Declaring and Calling Functions 34 Functions Are First-Class Objects 36 Anonymous Functions 38 *args and **kwargs 40 Decorators 42 Object-Oriented Programming 44 Class Definitions 44 Instantiation 45 Subclassing 46 Inner Classes 46 Regular Expressions 47 The re module 47 Searching Versus Matching 48 Common Gotchas 48 Single-Item Tuples 48 Modules 48 Mutability 50 Constructor Versus Initializer 52 Coding Style (PEP 8 and Beyond) 53 Indent Four Spaces 53 Use Spaces and Not Tabs 53 Don’t Write Single-Line Suites on the Same Line as the Header 54 Create Documentation Strings (aka “docstrings”) 54 Summary 2 Django for the Impatient: Building a Blog 55 57 Creating the Project 58 Running the Development Server 59 Creating the Blog Application 61 Designing Your Model 62 Setting Up the Database 62 Using a Database Server 63 Using SQLite 63 Creating the Tables Setting Up the Automatic admin Application www.it-ebooks.info 64 65 Trying Out the admin 66 Making Your Blog’s Public Side 70 Creating a Template 70 Creating a View Function 71 Creating a URL Pattern 72 Finishing Touches 73 Template Niceties 73 Date-Based Ordering 74 Timestamp Formatting Via a Template Filter 75 Summary 75 3 Starting Out 77 Dynamic Web Site Basics 77 Communication: HTTP URLs, Requests, , Responses 78 Data Storage: SQL and Relational Databases 78 Presentation: Rendering Templates into HTML and Other Formats 79 Putting It All Together 79 Understanding Models, Views, and Templates 79 Separating the Layers (MVC) 79 Models 80 Views 81 Templates 81 Overall Django Architecture 82 Core Philosophies of Django 82 Django Tries to Be Pythonic 84 Don’t Repeat Yourself (DRY) 84 Loose Coupling and Flexibility 84 Rapid Development 85 Summary 86 II: Django in Depth 4 Defining and Using Models Defining Models 89 89 Why Use an ORM? 89 www.it-ebooks.info Django’s Rich Field Types 91 Relationships Between Models 93 Model Inheritance 97 Meta Inner Class 100 Admin Registration and Options 101 Using Models 102 Creating and Updating Your Database Using manage.py 103 Query Syntax 104 Utilizing SQL Features Django Doesn’t Provide 112 Summary 5 URLs, HTTP Mechanisms, and Views URLs Introduction to URLconfs 116 117 117 117 Replacing Tuples with url 119 Using Multiple patterns Objects 119 Including Other URL Files with include 120 Function Objects Versus Function-Name Strings 121 Modeling HTTP: Requests, Responses, and Middleware 122 Request Objects 123 Response Objects 125 Middleware 126 Views/Logic 127 Just Python Functions 128 Generic Views 128 Semi-generic Views 130 Custom Views 131 Summary 133 6 Templates and Form Processing Templates 135 135 Understanding Contexts 135 Template Language Syntax 136 Forms Defining Forms www.it-ebooks.info 142 142 Filling Out Forms 147 Validation and Cleaning 149 Form Display 150 Widgets 152 Summary 154 III: Django Applications by Example 7 Photo Gallery 159 The Model 160 Preparing for File Uploads 161 Installing PIL 162 Testing ImageField 163 Building Our Custom File Field 164 Initialization 166 Adding Attributes to the Field 167 Saving and Deleting the Thumbnail 168 Using ThumbnailImageField 169 Setting Up DRY URLs 169 The Item App’s URL Layout 172 Tying It All Together with Templates 173 Summary 179 8 Content Management System 181 What’s a CMS? 181 The Un-CMS: Flatpages 182 Enabling the Flatpages App 182 Flatpage Templates 184 Testing It Out 184 Beyond Flatpages: A Simple Custom CMS Making the Model 185 186 Imports 188 Completing the Model 188 Controlling Which Stories Are Viewed 189 Working with Markdown 190 URL Patterns in urls.py 192 Admin Views 193 Displaying Content Via Generic Views 196 www.it-ebooks.info Template Layout 196 Displaying Stories 198 Adding Search 199 Managing Users 201 Supporting Workflow 202 Possible Enhancements 202 Summary 203 9 Liveblog 205 What Exactly Is Ajax? 205 Why Ajax Is Useful 206 Planning the Application 206 Choosing an Ajax Library 207 Laying Out the Application 208 Putting the Ajax In 211 The Basics 212 The “X” in Ajax (Or XML Versus JSON) 212 Installing the JavaScript Library 213 Setting Up and Testing jQuery 214 Creating the View Function 216 Using the View Function Via JavaScript 217 Summary 219 10 Pastebin 221 Defining the Model 222 Creating the Templates 223 Designing the URLs 225 Trying It Out 226 Limiting Number of Recent Pastes Displayed 229 Syntax Highlighting 230 Cleanup Via Cron Job 231 Summary 232 IV: Advanced Django Techniques and Features 11 Advanced Django Programming Customizing the Admin Changing Layout and Style Using Fieldsets www.it-ebooks.info 235 235 236 Extending the Base Templates 237 Adding New Views 238 Authentication Decorators 239 Using Syndication 240 The Feed Class 240 Giving the Feed a URL 242 Doing More with Feeds 242 Generating Downloadable Files 243 Nagios Configuration Files 243 vCard 244 Comma-Separated Value (CSV) 245 Charts and Graphs Using PyCha 246 Enhancing Django’s ORM with Custom Managers Changing the Default Set of Objects Adding New Manager Methods Extending the Template System 248 248 249 250 Simple Custom Template Tags 250 Inclusion Tags 253 Custom Filters 256 More Complex Custom Template Tags 258 Alternative Templating 258 Summary 260 12 Advanced Django Deployment Writing Utility Scripts 261 261 Cronjobs for Cleanup 262 Data Import/Export 263 Customizing the Django Codebase Itself 264 Caching 265 A Basic Caching Recipe 265 Caching Strategies 267 Caching Backend Types 272 Testing Django Applications 274 Doctest Basics 275 Unittest Basics 276 Running Tests 276 Testing Models 276 Testing Your Entire Web App 278 www.it-ebooks.info Testing the Django Codebase Itself Summary 279 281 V: Appendices A Command Line Basics Putting the “Command” in “Command Line” 285 285 Options and Arguments 288 Pipes and Redirection 289 Environment Variables 291 The Path 293 Summary 294 B Installing and Running Django Python 295 295 Mac OS X 296 Unix/Linux 296 Windows 296 Updating Your Path 296 Testing 299 Optional Add-ons 300 Django Packaged Releases 301 302 Development Version 302 Installation 302 Testing 303 Web Server The Built-In Server: Not for Production 303 303 The Standard Approach: Apache and mod_python 304 The Flexible Alternative: WSGI 306 Another Approach: Flup and FastCGI 307 SQL Database SQLite 308 308 PostgreSQL 309 MySQL 310 Oracle 311 Other Databases 311 Summary www.it-ebooks.info 311 C Tools for Practical Django Development Version Control 313 313 The Trunk and Branches 314 Merging 314 Centralized Version Control 315 Decentralized Version Control 315 Version Control for Your Project 316 Project Management Software Trac 318 319 Text Editors 319 Emacs 319 Vim 320 TextMate 320 Eclipse 320 D Finding, Evaluating, and Using Django Applications 321 Where to Look for Applications 321 How to Evaluate Applications 322 How to Use Applications 323 Sharing Your Own Application 323 E Django on the Google App Engine 325 Why the App Engine Matters 325 Pure Google App Engine Applications 326 Limitations of the App Engine Framework 326 Google App Engine Helper for Django 327 Getting the SDK and the Helper 327 More on the Helper 327 Integrating the App Engine 328 Copying the App Engine Code to Your Project 328 Integrating the App Engine Helper 329 Porting Your Application to App Engine 330 Taking a Test Drive 330 Adding Data 331 www.it-ebooks.info Creating a New Django Application That Runs on App Engine 333 Summary 334 Online Resources 334 F Getting Involved in the Django Project 337 Index 339 Colophon 375 www.it-ebooks.info This page intentionally left blank www.it-ebooks.info Preface Welcome to Django! Greetings, and welcome to Django! We’re glad to have you along on our journey.You will discover a powerful Web application framework that lets you do everything rapidly—from designing and developing the original application to updating its features and functionality without requiring major changes to the codebase. About This Book Several Django books are already on the market, but ours differs from most in that we focus equally on three areas: Django basics, a variety of example applications, and advanced Django topics. Our intent is to make this the most well-rounded book on the subject, one you find useful regardless of background, and which will give you a complete picture of the framework and what you can do with it. Chapter Guide In Figure 0.1, you see recommended starting points for your reading depending on your Python and Django experience. Of course, we recommend a cover-to-cover treatment, but the diagram will help if time is not on your side. Regardless of your experience, you are always welcome to look at the applications because reading and studying code is one of the best ways to learn.We also provide this chapter-by-chapter reading guide to further help direct you to where you need to read. Part I, “Getting Started” Part I covers the basic material needed to introduce users new to Django and/or Python, although we recommend Chapter 3, “Starting Out,” even to advanced readers. Chapter 1, “Practical Python for Django” This chapter is an introduction for readers who are new to Python. In one comprehensive chapter, we show you not only the syntax, but also go a bit more in-depth and expose you to Python’s memory model and data types, especially constructs commonly used in Django. www.it-ebooks.info Know Python but new to Django Brand New to Django and Python Know Python and some Django already Know Python and Django well but want advanced usage Chp 7 Photo Gallery Chp 8 CMS Chp 1 Practical Python Chp 2 Impatient (blog) Chp 9 Liveblog Chp 3 Starting Out Chp 10 Pastebin Part I: Getting Started Part III: Applications Chp 4 Models Chp 5 Views Chp 6 Templates Part II: Django in Depth Chp 11 Advanced Django Programming Chp 12 Advanced Django Deployment Appendices A-F Part IV: Advanced Figure 0.1 Suggested reading guide based on your Python and/or Django experience Chapter 2, “Django for the Impatient: Building a Blog” This is a chapter for those who want to skip any Python introduction and want to dive immediately into a Django application that can be completed in 15-20 minutes. It gives a good overview of what’s possible with the framework. Chapter 3, “Starting Out” For those with a bit more patience, this chapter serves as an introduction to all the foundations of developing Web-based applications (useful both for newbies and experienced www.it-ebooks.info coders alike). Once the formalities are over, we describe how each concept fits into the world of Django as well as what its philosophies are and how it may differ from other Web application frameworks. Part II, “Django in Depth” Part II covers all the basic components of the framework, laying the foundation for the example applications in Part III, “Django Applications by Example.” Chapter 4, “Defining and Using Models” In Chapter 4, learn how to define and work with your data model, including the basics of Django’s object-relational mapper (ORM) from simple fields up to complex relations. Chapter 5, “URLs, HTTP Mechanisms, and Views” This chapter goes into detail on how Django handles URL processing and the rest of the HTTP protocol, including middleware layers, as well as how to use Django’s timesaving generic views, and how to write custom or partially custom views from scratch. Chapter 6, “Templates and Form Processing” Chapter 6 covers the final major piece of the framework, where we explore Django’s template language and its form-handling mechanisms. It covers how to display data to your users and get data back from them. Part III, “Django Applications by Example” In Part III, we create four distinct applications, each highlighting a different aspect or component of Django development, both to introduce new general ideas and to expand on the concepts found in Parts I and II. Chapter 7, “Photo Gallery” In Chapter 7, learn how to apply the “Don’t Repeat Yourself ” convention to your URL structure and create a new thumbnail-creating image form field, while you make a simple photo gallery application. Chapter 8, “Content Management System” Chapter 8 contains two related approaches to creating a CMS or CMS-like system and covers the use of a number of “contrib” Django applications. Chapter 9, “Liveblog” Chapter 9 covers writing a “liveblog”—a site that makes use of advanced JavaScript techniques, serves as a backdrop for applying AJAX to a Django project, and shows how easy it is to use any AJAX toolkit you want. Chapter 10, “Pastebin” In Chapter 10, learn the power of Django’s generic views as we create a pastebin using almost no custom logic whatsoever. www.it-ebooks.info