Beginning Python (Peter C. Norton, Alex Samuel, Dave Aitel etc.) (Z-Library)

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Beginning Python 01_596543 ffirs.qxd 6/29/05 11:00 PM Page i

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Beginning Python Peter Norton, Alex Samuel, David Aitel, Eric Foster-Johnson, Leonard Richardson, Jason Diamond, Aleatha Parker, Michael Roberts 01_596543 ffirs.qxd 6/29/05 11:00 PM Page iii

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Beginning Python Published by Wiley Publishing, Inc. 10475 Crosspoint Boulevard Indianapolis, IN 46256 www.wiley.com Copyright © 2005 by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada ISBN-10: 0-7645-9654-3 ISBN-13: 978-0-7645-9654-4 Manufactured in the United States of America 10 9 8 7 6 5 4 3 2 1 1B/SQ/QX/QV/IN Library of Congress Cataloging-in-Publication Data: Beginning Python / Peter Norton. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-7645-9654-4 (paper/website) ISBN-10: 0-7645-9654-3 (paper/website) 1. Python (Computer program language) I. Norton, Peter, 1974- QA76.73.P98B45 2005 005.13’3--dc22 2005013968 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to the Publisher for permission should be addressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4355, or online at http://www.wiley.com/go/permissions. LIMIT OF LIABILITY/DISCLAIMER OF WARRANTY: THE PUBLISHER AND THE AUTHOR MAKE NO REPRESEN- TATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS WORK AND SPECIFICALLY DISCLAIM ALL WARRANTIES, INCLUDING WITHOUT LIMITATION WAR- RANTIES OF FITNESS FOR A PARTICULAR PURPOSE. NO WARRANTY MAY BE CREATED OR EXTENDED BY SALES OR PROMOTIONAL MATERIALS. THE ADVICE AND STRATEGIES CONTAINED HEREIN MAY NOT BE SUIT- ABLE FOR EVERY SITUATION. THIS WORK IS SOLD WITH THE UNDERSTANDING THAT THE PUBLISHER IS NOT ENGAGED IN RENDERING LEGAL, ACCOUNTING, OR OTHER PROFESSIONAL SERVICES. IF PROFESSIONAL ASSISTANCE IS REQUIRED, THE SERVICES OF A COMPETENT PROFESSIONAL PERSON SHOULD BE SOUGHT. NEITHER THE PUBLISHER NOR THE AUTHOR SHALL BE LIABLE FOR DAMAGES ARISING HEREFROM. THE FACT THAT AN ORGANIZATION OR WEBSITE IS REFERRED TO IN THIS WORK AS A CITATION AND/OR A POTENTIAL SOURCE OF FURTHER INFORMATION DOES NOT MEAN THAT THE AUTHOR OR THE PUBLISHER ENDORSES THE INFORMATION THE ORGANIZATION OR WEBSITE MAY PROVIDE OR RECOMMENDATIONS IT MAY MAKE. FURTHER, READERS SHOULD BE AWARE THAT INTERNET WEBSITES LISTED IN THIS WORK MAY HAVE CHANGED OR DISAPPEARED BETWEEN THEN THIS WORK WAS WRITTEN AND WHEN IT IS READ. For general information on our other products and services please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Trademarks: Wiley, the Wiley logo, Wrox, the Wrox logo, Programmer to Programmer, and related trade dress are trade- marks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates, in the United States and other countries, and may not be used without written permission. All other trademarks are the property of their respective owners. Wiley Publishing, Inc., is not associated with any product or vendor mentioned in this book. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. 01_596543 ffirs.qxd 6/29/05 11:00 PM Page iv

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About the Authors Peter Norton (NY, NY) has been working with Unix and Linux for over a decade at companies large and small solving problems with Linux. An officer of the NY Linux Users Group, he can be found on the nylug-talk mailing list. Peter coauthored Professional RHEL3. He works for a very large financial com- pany in NYC, plying his Python and open-source skills. Alex Samuel (San Diego, CA) has developed software for biology researchers and now studies high- energy physics at Caltech. Alex has worked on many GNU/Linux development tools, including GCC, and co-founded CodeSourcery LLC, a consulting firm specializing in GNU/Linux development tools. David Aitel (NY, NY) is the CEO of Immunity and a coauthor of Shellcoder’s Handbook. Eric Foster-Johnson (Minneapolis, MN) uses Python extensively with Java, and is a veteran author, most recently completing Beginning Shell Scripting. Leonard Richardson (San Francisco, CA) writes useful Python packages with silly names. Jason Diamond (CA) Jason Diamond is a software development instructor for DevelopMentor and a consultant specializing in C++, .NET, Python, and XML. He spends most of his spare time contributing to open-source projects using his favorite language, Python. Aleathea Parker (San Francisco CA) is a programmer working as a publication engineer for a major software company, coding primarily in Python and XSLT. She has a background in web applications and content management. Michael Roberts (Puerto Rico) has been programming professionally in C, Perl, and Python for long enough that Python didn’t actually exist when he started. He is the chief perpetrator of the wftk open-source workflow toolkit, and he swears that it will someday be finished, for certain values of “finished”. 01_596543 ffirs.qxd 6/29/05 11:00 PM Page v

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Credits Acquisitions Editor Debra Williams Cauley Development Editor Kelly D. Henthorne Production Editor William A. Barton Copy Editor Luann Rouff Production Manager Tim Tate Editorial Manager Mary Beth Wakefield Vice President & Executive Group Publisher Richard Swadley Vice President and Publisher Joseph B. Wikert Project Coordinator Kristie Rees Graphics and Production Specialists Sean Decker Carrie Foster Lauren Goddard Denny Hager Jennifer Heleine Amanda Spagnuolo Quality Control Technicians Leann Harney Joe Niesen Carl William Pierce Media Development Specialists Angela Denny Kit Malone Travis Silvers Proofreading and Indexing TECHBOOKS Production Services 01_596543 ffirs.qxd 6/29/05 11:00 PM Page vii

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To my Claudia, for keeping me thinking straight through a crazy time. To my mom, Eunice, for bringing me food and asking if I was okay throughout. To Debra, for roping me into this. And to all of the authors, I want to thank you for making it to the finish line. Whoa! I didn’t know what I was getting you all into! —P. N. To my dad, Clarence A. Johnson, 1922–2005. —E. F-J. For my mother. —L. R. For Jilly: 1 = 2. —J. D. To Aaron, for putting up with me. —A. P. To my wife, Agnes, in revenge for her doctoral thesis. —M. R. 01_596543 ffirs.qxd 6/29/05 11:00 PM Page ix

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Contents Acknowledgments xxix Introduction xxxi Chapter 1: Programming Basics and Strings 1 How Programming Is Different from Using a Computer 1 Programming Is Consistency 2 Programming Is Control 2 Programming Copes with Change 2 What All That Means Together 3 The First Steps 3 Starting codeEditor 3 Using codeEditor’s Python Shell 4 Try It Out: Starting the Python Shell 4 Beginning to Use Python — Strings 5 What Is a String? 5 Why the Quotes? 6 Try It Out: Entering Strings with Different Quotes 6 Understanding Different Quotes 6 Putting Two Strings Together 8 Try It Out: Using + to Combine Strings 8 Putting Strings Together in Different Ways 9 Try It Out: Using a Format Specifier to Populate a String 9 Try It Out: More String Formatting 9 Displaying Strings with Print 10 Try It Out: Printing Text with Print 10 Summary 10 Exercises 11 Chapter 2: Numbers and Operators 13 Different Kinds of Numbers 13 Numbers in Python 14 Try It Out: Using Type with Different Numbers 14 Try It Out: Creating an Imaginary Number 15 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xi

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xii Contents Program Files 15 Try It Out: Using the Shell with the Editor 16 Using the Different Types 17 Try It Out Including Different Numbers in Strings 18 Try It Out: Escaping the % Sign in Strings 18 Basic Math 19 Try It Out Doing Basic Math 19 Try It Out: Using the Modulus Operation 20 Some Surprises 20 Try It Out: Printing the Results 21 Using Numbers 21 Order of Evaluation 21 Try It Out: Using Math Operations 21 Number Formats 22 Try It Out: Using Number Formats 22 Mistakes Will Happen 23 Try It Out: Making Mistakes 23 Some Unusual Cases 24 Try It Out: Formatting Numbers as Octal and Hexadecimal 24 Summary 24 Exercises 25 Chapter 3: Variables — Names for Values 27 Referring to Data – Using Names for Data 27 Try It Out: Assigning Values to Names 28 Changing Data Through Names 28 Try It Out: Altering Named Values 29 Copying Data 29 Names You Can’t Use and Some Rules 29 Using More Built-in Types 30 Tuples — Unchanging Sequences of Data 30 Try It Out: Creating and Using a Tuple 30 Try It Out: Accessing a Tuple Through Another Tuple 31 Lists — Changeable Sequences of Data 33 Try It Out Viewing the Elements of a List 33 Dictionaries — Groupings of Data Indexed by Name 34 Try It Out: Making a Dictionary 34 Try It Out: Getting the Keys from a Dictionary 35 Treating a String Like a List 36 Special Types 38 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xii

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xiii Contents Other Common Sequence Properties 38 Referencing the Last Elements 38 Ranges of Sequences 39 Try It Out: Slicing Sequences 39 Growing Lists by Appending Sequences 40 Using Lists to Temporarily Store Data 40 Try It Out: Popping Elements from a List 40 Summary 41 Exercises 42 Chapter 4: Making Decisions 43 Comparing Values — Are They the Same? 43 Try It Out: Comparing Values for Sameness 43 Doing the Opposite — Not Equal 45 Try It Out: Comparing Values for Difference 45 Comparing Values — Which One Is More? 45 Try It Out: Comparing Greater Than and Less Than 45 More Than or Equal, Less Than or Equal 47 Reversing True and False 47 Try It Out: Reversing the Outcome of a Test 47 Looking for the Results of More Than One Comparison 48 How to Get Decisions Made 48 Try It Out: Placing Tests within Tests 49 Repetition 51 How to Do Something — Again and Again 51 Try It Out: Using a while Loop 51 Stopping the Repetition 52 Try It Out: Using else While Repeating 54 Try It Out: Using continue to Keep Repeating 54 Handling Errors 55 Trying Things Out 55 Try It Out: Creating an Exception with Its Explanation 56 Summary 57 Exercises 58 Chapter 5: Functions 59 Putting Your Program into Its Own File 59 Try It Out: Run a Program with Python -i 61 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xiii

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xiv Contents Functions: Grouping Code under a Name 61 Try It Out: Defining a Function 61 Choosing a Name 62 Describing a Function in the Function 63 Try It Out: Displaying __doc__ 63 The Same Name in Two Different Places 64 Making Notes to Yourself 65 Try It Out: Experimenting with Comments 65 Asking a Function to Use a Value You Provide 66 Try It Out Invoking a Function with Parameters 67 Checking Your Parameters 68 Try It Out: Determining More Types with the type Function 69 Try It Out: Using Strings to Compare Types 69 Setting a Default Value for a Parameter — Just in Case 70 Try It Out: Setting a Default Parameter 70 Calling Functions from within Other Functions 71 Try It Out: Invoking the Completed Function 72 Functions Inside of Functions 72 Flagging an Error on Your Own Terms 73 Layers of Functions 74 How to Read Deeper Errors 74 Summary 75 Exercises 76 Chapter 6: Classes and Objects 79 Thinking About Programming 79 Objects You Already Know 79 Looking Ahead: How You Want to Use Objects 81 Defining a Class 81 How Code Can Be Made into an Object 81 Try It Out: Defining a Class 82 Try It Out: Creating an Object from Your Class 82 Try It Out: Writing an Internal Method 84 Try It Out: Writing Interface Methods 85 Try It Out: Using More Methods 87 Objects and Their Scope 89 Try It Out: Creating Another Class 89 Summary 92 Exercises 93 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xiv

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xv Contents Chapter 7: Organizing Programs 95 Modules 96 Importing a Module So That You Can Use It 96 Making a Module from Pre-existing Code 97 Try It Out: Creating a Module 97 Try It Out: Exploring Your New Module 98 Using Modules — Starting With the Command Line 99 Try It Out: Printing sys.argv 100 Changing How Import Works — Bringing in More 101 Packages 101 Try It Out: Making the Files in the Kitchen Class 102 Modules and Packages 103 Bringing Everything into the Current Scope 103 Try It Out: Exporting Modules from a Package 104 Re-importing Modules and Packages 104 Try It Out: Examining sys.modules 105 Basics of Testing Your Modules and Packages 106 Summary 106 Exercises 107 Chapter 8: Files and Directories 109 File Objects 109 Writing Text Files 110 Reading Text Files 111 Try It Out: Printing the Lengths of Lines in the Sample File 112 File Exceptions 113 Paths and Directories 113 Paths 114 Directory Contents 116 Try It Out: Getting the Contents of a Directory 116 Try It Out: Listing the Contents of Your Desktop or Home Directory 118 Obtaining Information about Files 118 Recursive Directory Listings 118 Renaming, Moving, Copying, and Removing Files 119 Example: Rotating Files 120 Creating and Removing Directories 121 Globbing 122 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xv

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xvi Contents Pickles 123 Try It Out: Creating a Pickle File 123 Pickling Tips 124 Efficient Pickling 125 Summary 125 Exercises 125 Chapter 9: Other Features of the Language 127 Lambda and Filter: Short Anonymous Functions 127 Reduce 128 Try It Out: Working with Reduce 128 Map: Short-Circuiting Loops 129 Try It Out: Use Map 129 Decisions within Lists — List Comprehension 130 Generating Lists for Loops 131 Try It Out: Examining an xrange Object 132 Special String Substitution Using Dictionaries 133 Try It Out: String Formatting with Dictionaries 133 Featured Modules 134 Getopt — Getting Options from the Command Line 134 Using More Than One Process 137 Threads — Doing Many Things in the Same Process 139 Storing Passwords 140 Summary 141 Exercises 142 Chapter 10: Building a Module 143 Exploring Modules 143 Importing Modules 145 Finding Modules 145 Digging through Modules 146 Creating Modules and Packages 150 Try It Out: Creating a Module with Functions 150 Working with Classes 151 Defining Object-Oriented Programming 151 Creating Classes 151 Try It Out: Creating a Meal Class 152 Extending Existing Classes 153 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xvi

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xvii Contents Finishing Your Modules 154 Defining Module-Specific Errors 154 Choosing What to Export 155 Documenting Your Modules 156 Try It Out: Viewing Module Documentation 157 Testing Your Module 162 Running a Module as a Program 164 Try It Out: Running a Module 164 Creating a Whole Module 165 Try It Out: Finishing a Module 165 Try It Out: Smashing Imports 169 Installing Your Modules 170 Try It Out: Creating an Installable Package 171 Summary 174 Exercises 174 Chapter 11: Text Processing 175 Why Text Processing Is So Useful 175 Searching for Files 176 Clipping Logs 177 Sifting through Mail 178 Navigating the File System with the os Module 178 Try It Out: Listing Files and Playing with Paths 180 Try It Out: Searching for Files of a Particular Type 181 Try It Out: Refining a Search 183 Working with Regular Expressions and the re Module 184 Try It Out: Fun with Regular Expressions 186 Try It Out: Adding Tests 187 Summary 189 Exercises 189 Chapter 12: Testing 191 Assertions 191 Try It Out: Using Assert 192 Test Cases and Test Suites 193 Try It Out: Testing Addition 194 Try It Out: Testing Faulty Addition 195 Test Fixtures 196 Try It Out: Working with Test Fixtures 197 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xvii

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xviii Contents Putting It All Together with Extreme Programming 199 Implementing a Search Utility in Python 200 Try It Out: Writing a Test Suite First 201 Try It Out: A General-Purpose Search Framework 203 A More Powerful Python Search 205 Try It Out: Extending the Search Framework 206 Formal Testing in the Software Life Cycle 207 Summary 208 Chapter 13: Writing a GUI with Python 209 GUI Programming Toolkits for Python 209 PyGTK Introduction 210 pyGTK Resources 211 Creating GUI Widgets with pyGTK 213 Try It Out: Writing a Simple pyGTK Program 213 GUI Signals 214 GUI Helper Threads and the GUI Event Queue 216 Try It Out: Writing a Multithreaded pyGTK App 219 Widget Packing 222 Glade: a GUI Builder for pyGTK 223 GUI Builders for Other GUI Frameworks 224 Using libGlade with Python 225 A Glade Walkthrough 225 Starting Glade 226 Creating a Project 227 Using the Palette to Create a Window 227 Putting Widgets into the Window 228 Glade Creates an XML Representation of the GUI 230 Try It Out: Building a GUI from a Glade File 231 Creating a Real Glade Application 231 Advanced Widgets 238 Further Enhancing PyRAP 241 Summary 248 Exercises 248 Chapter 14: Accessing Databases 249 Working with DBM Persistent Dictionaries 250 Choosing a DBM Module 250 Creating Persistent Dictionaries 251 Try It Out: Creating a Persistent Dictionary 251 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xviii

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xix Contents Accessing Persistent Dictionaries 252 Try It Out: Accessing Persistent Dictionaries 253 Deciding When to Use DBM and When to Use a Relational Database 255 Working with Relational Databases 255 Writing SQL Statements 257 Defining Tables 259 Setting Up a Database 260 Try It Out: Creating a Gadfly Database 261 Using the Python Database APIs 262 Downloading Modules 263 Creating Connections 263 Working with Cursors 264 Try It Out: Inserting Records 264 Try It Out: Writing a Simple Query 266 Try It Out: Writing a Complex Join 267 Try It Out: Updating an Employee’s Manager 269 Try It Out: Removing Employees 270 Working with Transactions and Committing the Results 271 Examining Module Capabilities and Metadata 272 Handling Errors 272 Summary 273 Exercises 274 Chapter 15: Using Python for XML 275 What Is XML? 275 A Hierarchical Markup Language 275 A Family of Standards 277 What Is a Schema/DTD? 278 What Are Document Models For? 278 Do You Need One? 278 Document Type Definitions 278 An Example DTD 278 DTDs Aren’t Exactly XML 280 Limitations of DTDs 280 Schemas 280 An Example Schema 280 Schemas Are Pure XML 281 Schemas Are Hierarchical 281 Other Advantages of Schemas 281 Schemas Are Less Widely Supported 281 02_596543 ftoc.qxd 6/29/05 10:55 PM Page xix