XML Processing with Python

Description

• Copyright 2000
• Edition: 1st

• Book
• ISBN-10: 0-13-021119-2
• ISBN-13: 978-0-13-021119-4

• Breakthrough techniques for building XML applications — fast!
• Includes a detailed Python tutorial
• Learn about DOM and SAX application development with Python
• Exclusive coverage of the new Pyxie XML processing library
• CD-ROM includes Python and Pyxie distributions for Windows NT and Linux—plus powerful utilities and lots of working code

"XML processing is the newest required skill for webmasters and application developers. The Python language and Sean McGrath's book make it fun to learn and easy to do."
— Charles F. Goldfarb

When it comes to XML processing, Python is in a league of its own.

If you're doing XML development without Python, you're wasting time! Python offers outstanding productivity — especially in the areas that matter most to XML developers, such as XML parsing, DOM/SAX implementations, string processing, and Internet APIs.

And now there's Pyxie — the new open source library that makes Python XML processing even easier and more powerful. In XML Processing with Python, top XML developer Sean McGrath delivers the hands-on explanations and examples you need to get results with Python and Pyxie fast — even if you've never used them before!

• Install Python and the Pyxie XML package
• Learn the fundamentals of Python: control structures, classes, nested lists, dictionaries, and regular rexpresions
• Process XML with regular expression-driven, event-driven, and tree-driven techniques
• Understand Python's support for DOM and SAX APIs
• Explore the power of Python/XML through worked examples of GUI development, database integration, and an XML query-by-example implementation.

Elegant, easy, powerful and fun, Python helps you build world-class XML applications in less time than you ever imagined. If you know XML, one book has all the techniques, code, and tools you'll need to process it: XML Processing with Python.

CD-ROM INCLUDED

The accompanying CD-ROM contains everything you need to develop XML applications with Python — including

• complete Python distributions for Windows and Linux
• the Pyxie open-source libraries
• powerful utility programs
• an extensive library of sample source code tested on both Windows NT and Linux

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xMail: E-mail as XML

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Table of Contents

1. Introduction.

Purpose of This Book. The Pyxie Open Source Project. Prerequisites. How to Read This Book. A Note about Platforms. Structure of Code Samples. And Finally.

2. Installing Python.

Getting a Python Distribution. Installing the Software. Testing the Python Installation. Using a Python Program File. In Conclusion.

3. Installing the XML Package.

Testing the XML Package Installation. Testing the pyExpat Module. Testing SAX Support.

4. Tools of the Trade.

The xmln and xmlv Parsing Utilities. Simple XML-Processing Tasks with xmln and xmlv. The GetURL Utility-A Web Resource Retriever in Python. The PYX2XML Utility: Converting PYX to XML. The C3 Utility: An XML Document Editor/Viewer in Python. In Conclusion.

5. Just Enough Python.

Introduction. Basic Control Structures. Functions. Modules. Data Structures. Object Orientation. Design Principles. In Conclusion.

6. Some Important Details.

Dealing with Long Lines. Using the dir Function. Working with Docstrings. Importing Modules. Executing Python Programs. Using the Special Object None. Memory Management. Copying Objects. Determining Object Identity. Handling Errors. The Dynamic Nature of Python. Named Parameters. The Pass Statement. Packages.

7. Processing XML with Regular Expressions.

Command-Line Arguments. A Module Test Harness for xgrep. What If There Are No Command-Line Parameters? Adding Support for Wildcards. Parsing Command-Line Options. A Pattern-Matching Dry Run. Introducing Regular Expressions. Using Escape Sequences in Regular Expressions. Compiling Regular Expressions. Adding Regular Expressions to xgrep. xgrep in Action. Parsing XML with Regular Expressions. Cautionary Tales. Avoiding False Positive Matches. Shallow Parsing XML with Python Regular Expressions. Current Implementation of xgrep.

8. Event-driven XML Processing.

Making xgrep XML-Aware. Invoking xmln from xgrep. Adding PYX Support for xgrep. Adding XML Search Features to xgrep. Using Long Option Names in getopt. Using "Bit Twiddling" to Handle the Many Options Available. The Match Printing Function. Some Examples. Generalizing the Idea of Event-Based XML Processing. A Standardized Event-Driven Processing Model. Advantages and Disadvantages of Event-Driven Processing. In Conclusion.

9. Tree-driven XML Processing.

Modelling a Node. Navigating a Tree. Building xTree Structures. Building an xTree By Using PYX. A Test Harness for Pyxie. Handling Line Ends. A Syntax for Tree Processing with xgrep. Adding Support for Attributes. Some Utility Bits and Pieces. Implementing XMLGrepTree. A Standardized Tree-Driven XML Processing Model. Advantages and Disadvantages of Tree-Driven XML Processing. Some Examples. Bringing It All Together.

10. Just Enough SAX.

History. The Concept of an "Interface". Overview of the SAX Specification. The HandlerBase Class. The DocumentHandler Interface. The AttributeList Interface. The ErrorHandler Interface. A SAX Inspection Application. SAX as a Source of PYX. Switching SAX Parsers.

11. Just Enough DOM.

History. DOM Support in Python. The DOM Architecture. Accessing an XML File with pyDOM. Navigating a DOM Tree. Walking a DOM Tree. Accessing Attributes. Manipulating Trees. Accessing an HTML File with pyDOM. Printing the Text of an HTML Document. Changing Data Content in a DOM Tree. Creating a Tree Programmatically. Converting HTML to PYX by Using DOM. Using PYX as a DOM Data Source.

12. Pyxie: An Open Source XML- Processing Library for Python.

What Is Pyxie? Design Goals. PYX Notation Processing. Event-driven Processing. Tree-driven Processing. Tree Navigation. Tree Cut-and-Paste. Node Lists. Tree Walking. Hybrid Event- or Tree-driven Processing. The Invoice Printing Problem Solved Three Ways. The Complete Source Code for the Pyxie Library.

13. xFS: Filesystem Information in XML.

A Simple XML DTD for Filesystem Information. Some Python Features Used in the xFS Application. Viewing xFS Data with the C3 XML Editor/Viewer. Performing Filesystem Queries with xgrep. Source Code for xFS.

14. xMail: E-mail as XML.

The rfc822 Module. A Simple DTD for E-mail. An Example of an E-mail Message in XML. Processing a Eudora Mailbox. Processing a Linux Mailbox. Processing an E-mail Message by Using the rfc822 Module. Sending E-mail by Using xMail. Source Code for the SendxMail Application. Source Code for the xMail Application.

15. xMySQL: Relational Database Harvesting with Python SAX.

Installing MySQL. Testing the MySQL Installation. Installing the Python Interface to MySQL. Testing the Python Interface to MySQL. Mapping Relational Data to XML. The Python SAX Driver Interface. Implementing a SAX Driver for MySQL. A Template for SAX Drivers. The MySQL SAX Driver. Some Examples.

16. xTract: A Query-By-Example XML Retrieval System.

Expressing XML Queries. The xTract.py Utility in Action. xTract Version 1 Source Code. Handling Large XML Files with xTract. Source Code for the xTract1 Utility.

17. The C3 XML Editor/Viewer.

Developing wxPython Applications. A "Hello World" wxPython Application. Converting an xTree to a wxTree, and Vice Versa. Dynamic Module Loading. The Complete Source Code for C3.

Appendix A: An Overview of Python for Java Programmers.

Comparing the Python and Java Programming Languages.

Appendix B: An Overview of Python for Perl Programmers.


Index.

Preface

Introduction

XML is everywhere on the Web these days. Structured data of all shapes and sizes such as financial transactions, news feeds, health care records, even HTML is metamorphosing into XML. There is just no getting away from it!

I'm glad actually. The fact that XML is everywhere is a fundamentally good thing in my opinion.

Why? Well, thanks to XML, the Web is in transition from an enormous repository of display-oriented, unstructured, low-level data (HTML) into a repository of structured, heterogenous, content-oriented information (XML). This new, improved World Wide Web, housed on a bedrock of XML, presents programmers with awesome opportunities for innovative software development.

This suits me just fine because software development is what I like to do--even more than writing books about software development.

The fact that the "L" in XML stands for "Language" has been the source of some confusion. It is important to remember that XML is a data representation technology. It is not, by any stretch of the imagination, a programming language. Its strength lies in its ability to simply and cleanly represent complex hierarchical data structures. As you know, XML is a World Wide Web Consortium (W3C) recommendation for structured data representation. There is no such thing as a W3C-recommended XML programming language. Choice of a programming tool is entirely within the hands of the individual developer. In making a selection, an embarrassment of riches presents itself to us. We have the Java programming language, Perl, Tcl, C++, C, JavaScript, Visual Basic, Delphi, and of course Python. Each language has its benefits and its drawbacks as an XML-processing tool.

How to choose?

Well, choosing a programming language is an inexact science at best and is influenced by many factors that are technical, commercial, emotional, futuristic and political in nature. Even serendipity has a role to play.

For my part, standing here (actually sitting here) at the start of the 21st century, I can safely say, without fear of contradiction, that no programming language I know comes close to Python for XML processing.

"Strong words," you may say, but then again, I am only speaking about the languages I know, not the ones I don't.

Enough said! We are not here to engage in programming language wars—that is what Usenet is for. Suffice it to say that Python is a solidly engineered, general-purpose programming language with a natural affinity for text processing in general and XML processing in particular. Mix XML and Python together and you have an explosive cocktail of information representation and information processing power.

In my opinion . . .

1.1 - Purpose of This Book

This book has essentially one purpose: To give you all the information, explanations, working examples, and software packages (on the accompanying CD-ROM) you need to start writing XML-processing applications in Python fast.

This book will not slow you down with intricate technical details of either Python or XML. That is not to say that these things are not important! They are very important, but they are not discussed in this book. The reason for this omission is that I believe a pragmatic treatment of a subject such as Python/XML is the best way to become productive quickly. I believe that comprehensive coverage of the details too early on in the exploration of a topic like this just gets in the way. So, in this book, comprehensive coverage takes second place to working examples of real-world Python/XML programming. I will provide plenty of pointers to more detailed information for those of you who wish to dig deeper.

1.2 - The Pyxie Open Source Project

This book heralds the beginning of the Pyxie project—an Open Source software development initiative aimed at fully developing Python's potential as an XML-processing platform.

By the time you read this, the Pyxie project will have been launched at http://www.pyxie.org. It contains all the source code from this book along with more demo programs and applications for Windows and Linux.

There is a mailing list for Pyxie. To subscribe, send e-mail to pyxie-request@starship.python.net with the word subscribe in the body of the e-mail.

Get involved!

1.3 - Prerequisites

This book assumes that you have a high-level understanding of the ideas and syntax of XML. In particular, it would be helpful if you know the following:

• What an element is
• What start-tags and end-tags look like
• What the term "well formed XML" means
• What a DTD (Document Type Definition) is for

If you feel the need to brush up your XML, you might like to read my book XML by Example: Building eCommerce Applications available in this series.

This book assumes that you have some previous programming experience in a high-level language. Some exposure to object-oriented programming is desirable but not critical. If you have any exposure at all to the Java programming language, Perl, awk, Tcl, C++, C, JavaScript, Visual Basic, Delphi, or shell scripting languages, you are in good shape to attack this book.

If your programming background is minimal, fear not! Python is a ridiculously easy programming language to learn. Indeed, it makes an excellent first programming language for those approaching the discipline afresh.

If you are a seasoned programmer in one or more languages, I believe you will be pleasantly surprised at how easy, natural, and (okay, I'll say it) beautiful Python is.

1.4 - How to Read This Book

This book is intended to be read from start to finish. One of the techniques I have used to avoid long tracts of narrative about Python language features or support libraries is that I explain them as they pop up in the course of writing real programs.

As a consequence, skipping material might lead to gaps in the presentation of Python features. Even if you are very familiar with the subject matter in a section of the book, please give it a high-level scan to ensure that you pick up on any Python nuggets buried inside.

If your background is Java, you might like to read Appendix A before continuing. It introduces Python from a Java programming language perspective. Similarly, you might like to read Appendix B at this point if your background is in the Perl programming language.

1.5 - A Note about Platforms

My day-to-day programming environment is a mixture of Windows NT 4.0 and Red Hat Linux 6.0. These are the two platforms that the software presented in this book has been developed and tested on.

Although the book focuses on Windows NT and Linux, the Python programs in the book and in the CD-ROM's root directory should run just fine on any Win32 or Unix platform. There will obviously be the usual assortment of differences to do with default installation directories, differing shells, and so on. I have not attempted to cover all the eventualities in this book. To do so would make it twice as long and ten times more tedious to read.

1.7 - And Finally ...

I am a programmer who learns best by example. If this is a reasonable description of how you learn best, you are in the right place.

If you have read this far, you will have surmised that this book is going to take a no-nonsense, snappy, and purposeful approach to XML processing with Python.

Ready? Let's go to work ...

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