Hello! Python. Anthony Briggs MANNING SHELTER ISLAND

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2 Hello! Python

4 Hello! Python Anthony Briggs MANNING SHELTER ISLAND

5 For online information and ordering of this and other Manning books, please visit The publisher offers discounts on this book when ordered in quantity. For more information, please contact: Special Sales Department Manning Publications Co. 20 Baldwin Road PO Box 261 Shelter Island, NY by Manning Publications Co. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by means electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in the book, and Manning Publications was aware of a trademark claim, the designations have been printed in initial caps or all caps. User Friendly artwork, characters, and strips used by permission from UserFriendly.Org. All Rights Reserved. Recognizing the importance of preserving what has been written, it is Manning s policy to have the books we publish printed on acid-free paper, and we exert our best efforts to that end. Recognizing also our responsibility to conserve the resources of our planet, Manning books are printed on paper that is at least 15 percent recycled and processed without elemental chlorine. Development editor: Sebastian Stirling Manning Publications Co. Technical proofreader: Marion Newlevant 20 Baldwin Road Copyeditors: June Eding, Tiffany Taylor PO Box 261 Typesetter: Marija Tudor Shelter Island, NY Cover designer: Leslie Haimes ISBN: Printed in the United States of America MAL

6 Brief contents 1 WHY PYTHON? 1 2 HUNT THE WUMPUS 28 3 INTERACTING WITH THE WORLD 70 4 GETTING ORGANIZED 99 5 BUSINESS-ORIENTED PROGRAMMING CLASSES AND OBJECT-ORIENTED PROGRAMMING SUFFICIENTLY ADVANCED TECHNOLOGY DJANGO! GAMING WITH PYGLET TWISTED NETWORKING DJANGO REVISITED! WHERE TO FROM HERE? 383 v

8 Contents Foreword xv Preface xvii Acknowledgments xix About this book xxi About Hello! books xxv 1 Why Python? 1 Learning to program 2 Telling a computer what to do 3 Programming is made of ideas 5 Programming is design 5 What makes Python so great? 7 Python is easy 7 Python is a real language 8 Python has batteries included 8 Python has a large community 9 Setting up Python for Windows 9 Installing Python 9 Running Python programs on Windows 12 Running Python programs from the command line 14 Linux 18 Installing under Linux 18 Linux GUI 18 Linux command line 20 Macintosh 21 Updating the shell profile application Setting the default Troubleshooting 23 A syntax error 24 An incorrect file extension (Windows) 24 Python is installed in a different place (Linux) 24 vii

9 viii Contents Text editors and IDEs 24 Summary 26 2 Hunt the Wumpus 28 What s a program? 29 Writing to the screen 30 Remembering things with variables 31 Asking the player what to do 32 Making decisions 32 Loops 34 Functions 35 Your first program 36 The first version of Hunt the Wumpus 37 Debugging 39 Experimenting with your program 40 More (or fewer) caves 40 A nicer wumpus 40 More than one wumpus 41 Making the caves 41 Lists 42 For loops 44 Coding your caves 44 Fixing a more subtle bug 47 The problem 47 The solution 48 Coding connected caves 48 Clean up your code with functions! 51 Function basics 51 Variable scope 53 Shared state 54 Fixing the wumpus 55 Interacting with the caves 56 Creating the caves 57 Interacting with the player 59 The rest of the program 60 Bows and arrows 62 More atmosphere 65 Where to from here? 68 Bats and pits 68 Making the wumpus move 68 Different cave structures 69 Summary 69 3 Interacting with the world 70 Batteries included : Python s libraries 71 Python s standard library 72 Other libraries 72 Using libraries 72 What s in a library, anyway? 74

10 Contents ix Another way to ask questions 77 Using command-line arguments module Using the sys Reading and writing files 79 Paths and directories (a.k.a. dude, where s my file?) 79 Paths 81 File, open! 82 Comparing files 83 Fingerprinting a file 83 Mugshots: storing your files fingerprints in a dictionary 85 Putting it all together 86 Testing your program 91 Improving your script 93 Putting results in order 93 Comparing directories 95 Where to from here? 97 Summary 98 4 Getting organized 99 Planning: specifying your program 100 How do you know your program works? 101 Testing manually boring! 101 Functional testing 102 Unit testing: make the computer do it 102 Test-Driven Development 102 Writing the program 103 Making your tests pass 105 Putting your program together 107 Testing user interfaces 107 What do you do with your input? 109 Running commands 110 Running your program 113 Taking stock 114 What to do next? 115 I m very busy and important 118 List comprehensions 119 Oops, a bug! 122 Saving your work 127 Editing and deleting 131 A quick fix 131 Deleting to-dos 134 Editing to-dos 137

Florian Müller Jay Brown Jeff Potts. FOREWORDS BY Richard J. Howarth John Newton MANNING.

Florian Müller Jay Brown Jeff Potts FOREWORDS BY Richard J. Howarth John Newton MANNING CMIS and Apache Chemistry in Action CMIS and Apache Chemistry in Action FLORIAN MÜLLER JAY BROWN JEFF POTTS MANNING