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  • CherryPy Essentials

    Rapid Python Web Application Development

    Design, develop, test, and deploy your Python web applications easily

    Sylvain Hellegouarch


  • CherryPy Essentials Rapid Python Web Application Development

    Copyright © 2007 Packt Publishing

    All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

    Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, Packt Publishing, nor its dealers or distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

    Packt Publishing has endeavored to provide trademark information about all the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

    First published: March 2007

    Production Reference: 2220307

    Published by Packt Publishing Ltd. 32 Lincoln Road Olton Birmingham, B27 6PA, UK.

    ISBN �7�-�-�0����-��-��7�-�-�0����-��-�

    Cover Image by

  • Credits


    Sylvain Hellegouarch


    Rémi Delon

    Robert Brewer

    Development Editor

    Nanda Padmanabhan

    Technical Editors

    Saurabh Singh

    Shayantani Chaudhuri

    Ved Prakash Jha

    Editorial Manager

    Dipali Chittar

    Project Manager

    Patricia Weir

    Project Coordinator

    Sagara Naik


    Bhushan Pangaonkar


    Chris Smith

    Layouts and Illustrations

    Shantanu Zagade

    Manjiri Nadkarni

    Cover Designer

    Shantanu Zagade

  • About the Author

    Sylvain Hellegouarch is an IT Software Consultant dedicated to the development of free software projects such as CherryPy. Since 200�, he has been coordinating and administrating the community efforts around the project providing support for newcomers and seasoned developers, alike. In 2006, he developed 'bridge' and 'amplee', two Python-based projects centered on XML and the upcoming Atom Publishing Protocol respectively.

    He has also been deeply involved in The Viberavetions Project, a comprehensive grassroots solution for independent artists and musicians to better connect with consumers, as well as the nuXleus project, a platform designed for faster, more reliable inter- and intra-application and personal communication.

    Born in France, Sylvain graduated with a degree in Computer Science from South Brittany University, Lorient, France in 2002. Since then he has been working as an IT consultant for a variety of companies, both small and large. He currently resides in the United Kingdom.

  • Acknowledgement

    Throwing myself into the adventure of writing a book was a challenge I had in mind for a while before Packt Publishing came along and I do thank them for trusting me on the CherryPy book. Overall writing a book is a task you can't carry alone; editors and reviewers are critical to the release of a good quality book. I thoroughly thank Robert Brewer and Rémi Delon for undertaking the task of reviewing my work and I much appreciate how difficult it has been. Both contributed complementary feedback that hopefully will make you enjoy reading this book. Beyond that I want to thank Robert for making CherryPy such a fantastic product to use; I hope this book will show how professional CherryPy is. Of course all of this would not have been possible if Rémi, the founder of the project, had not given the keys and his full trust to the community for carrying the project. In addition I would like to thank Christian Wyglendowski who has done a fantastic job at supporting the community for so long with such indulgence and sense of humor. I would also like to give thanks to my contacts at Packt Publishing, Nanda Padmanabhan, Patricia Weir, and Suneet Amrute for their support and patience throughout the making of this book. They have trusted me and listened to my concerns in a way that I can only be grateful for.

    I also want to acknowledge the support I received from folks at the Viberavetions project especially M. David Peterson who has become a close friend, without forgetting Uche Ogbuji, Russ Miles and Kurt Cagle who have all shared their views at times when I needed them.

    I heartily want to thank all my friends who have always respected my passion for being part of open-source projects and communities while reminding me that there is more to life than lines of code. They have been a breath of fresh air to me throughout these years and a great comfort when times weren't good: one person particularly who has taken a great place in my life and who has always pushed me ahead.

    Lastly I want to deeply thank my beloved family for always being discreetly there for me and supporting my decisions even when they did not look like they were in my best interests. You have never failed me and the work I have put into this book is a way for me to thank you for that. Merci à vous.

    This book is for the CherryPy community and beyond.

  • About the Reviewers

    Rémi Delon is a French software developer and entrepreneur living in London, UK. He has been developing software for over �0 years and contributing to the open-source community for over five years. He is the original creator of CherryPy and is now running WebFaction, a fast growing hosting service specialized in agile tools, including CherryPy and TurboGears.

    Robert Brewer is the System Architect for Amor Ministries, a non-profit house-building ministry that serves the poors of Mexico.

    He is the lead developer of the CherryPy project, and wrote most of version 3.0. He is also the author of the modpython gateway for WSGI, and is the creator of Dejavu, a pure-Python Object-Relational Mapper.

    Founded in 2003 by the original CherryPy creator, WebFaction is a reliable and affordable hosting provider for your CherryPy applications. You can get an exclusive 20% discount by using the promo code "CHERRYPYBOOK" when you sign up with WebFaction, visit for more details.

  • Table of Contents Preface 1 Chapter 1: Introduction to CherryPy 7

    Overview 7 History of CherryPy 8 The Community 9 CherryPy Project Strengths 10 Beyond CherryPy 11 Through the Book 11 Summary 12

    Chapter 2: Download and Install CherryPy 13 Requirements 13 Overview 14 Installation from a Tarball 16 Installation through Easy Install 18 Installation from Subversion 20 Testing your Installation 23 Keeping CherryPy Up to Date 23 Summary 24

    Chapter 3: Overview of CherryPy 25 Vocabulary 25 Basic Example 26 Built-In HTTP Server 32 Internal Engine 32 Configuration 33 Object Publisher Engine 36 Library 38

    The Autoreload Feature 39 The Caching Module 39

  • Table of Contents

    [ ii ]

    The Coverage Module 39 The Encoding/Decoding Module 40 The HTTP Module 40 The Httpauth Module 40 The Profiler Module 40 The Sessions Module 41 The Static Module 42 The Tidy Module 42 The Wsgiapp Module 42 The XML-RPC Module 42

    Tools 43 Error and Exception Handling 44 Summary 49

    Chapter 4: CherryPy in Depth 51 HTTP Compliance 51 Multiple HTTP Servers 52 Multi-Threaded Application Server 54 URI Dispatching 55

    HTTP Method Dispatcher 55 Routes Dispatcher 57 Virtual Host Dispatcher 58

    Hook into CherryPy's Core Engine 59 CherryPy Toolbox 61

    Basic Authentication Tool 62 Caching Tool 63 Decoding Tool 64 Digest Authentication Tool 65 Encode Tool 66 Error Redirect Tool 67 Etag Tool 67 Gzip Tool 69 Ignore Headers Tool 69 Log Headers Tool 70 Log Tracebacks Tool 71 Proxy Tool 72 Referer Tool 73 Response Headers Tool 74 Trailing Slash Tool 75 XML-RPC Tool 76 Toolbox 77 Creating a Tool 77

  • Table of Contents

    [ iii ]

    Static Resource Serving 81 Using the Staticfile Tool to Serve a Single File 81 Using the Staticdir Tool to Serve a Complete Directory 83 Bypassing Static Tools to Serve Static Content 85

    WSGI Support 86 Hosting a WSGI Application within the CherryPy WSGI Server 87 Hosting a CherryPy WSGI Application within a Third-Party WSGI Server 89

    Summary 90 Chapter 5: A Photoblog Application 91

    A Photoblog Application 91 Photoblog Entities 92 Vocabulary 94 DBMSes Overview 95

    Relational Database Management System (RDBMS) 95 Object-Oriented Database Management System (OODBMS) 96 XML Database Management System (XMLDBMS) 97

    Object-Relational Mapping 97 Python Object-Relational Mappers 98

    Photoblog Application Entity Modeling 108 Mapping Entities 109 Units and UnitProperties 111 Associating Units 112 The Sandbox Interface 112

    Querying Units 113 Extending the Data Access Layer 114 Summary 117

    Chapter 6: Web Services 119 Traditional Web Development 119

    Separation of Concerns 121 REST 122 Uniform Resource Identifier 123 HTTP Methods 124 Putting it Together 128 REST Interface through CherryPy 130 Atom Publishing Protocol 131 Atom XML-Document Format 132 APP Implementation 134 Summary 136

  • Table of Contents

    [ iv ]

    Chapter 7: