Python Cookbook 3rd Edition 2013.pdf

THIRD EDITION

Python Cookbook

David Beazley and Brian K. Jones

Python Cookbook, Third Edition

by David Beazley and Brian K. Jones

Printed in the United States of America.

Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.

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Cover Designer: Karen Montgomery

Interior Designer: David Futato

Illustrator: Robert Romano

May 2013:

Third Edition

Revision History for the Third Edition:

2013-05-08:

First release

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no responsibility for errors or omissions, or for damages resulting from the use of the information contained

herein.

ISBN: 978-1-449-34037-7

[LSI]

Table of Contents

Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Data Structures and Algorithms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1. Unpacking a Sequence into Separate Variables 1

1.2. Unpacking Elements from Iterables of Arbitrary Length 3

1.3. Keeping the Last N Items 5

1.4. Finding the Largest or Smallest N Items 7

1.5. Implementing a Priority Queue 8

1.6. Mapping Keys to Multiple Values in a Dictionary 11

1.7. Keeping Dictionaries in Order 12

1.8. Calculating with Dictionaries 13

1.9. Finding Commonalities in Two Dictionaries 15

1.10. Removing Duplicates from a Sequence while Maintaining Order 17

1.11. Naming a Slice 18

1.12. Determining the Most Frequently Occurring Items in a Sequence 20

1.13. Sorting a List of Dictionaries by a Common Key 21

1.14. Sorting Objects Without Native Comparison Support 23

1.15. Grouping Records Together Based on a Field 24

1.16. Filtering Sequence Elements 26

1.17. Extracting a Subset of a Dictionary 28

1.18. Mapping Names to Sequence Elements 29

1.19. Transforming and Reducing Data at the Same Time 32

1.20. Combining Multiple Mappings into a Single Mapping 33

Strings and Text. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.1. Splitting Strings on Any of Multiple Delimiters 37

2.2. Matching Text at the Start or End of a String 38

2.3. Matching Strings Using Shell Wildcard Patterns 40

2.4. Matching and Searching for Text Patterns 42

iii

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