Python 3 Object Oriented Programming

Dusty Phillips

• Publisher: Packt Publishing
• Year: 2010
• eBook ISBN: 9781849511261
• Edition: 1
• Topic: Informatik
• Subtopic: Programmierung in Python

In Detail

Object Oriented Programming is a very important aspect of modern programming languages. The basic principles of Object Oriented Programming are relatively easy to learn. Putting them together into working designs can be challenging.

This book makes programming more of a pleasure than a chore using powerful Python 3 object-oriented features of Python 3. It clearly demonstrates the core OOP principles and how to correctly implement OOP in Python.

Object Oriented Programming ranks high in importance among the many models Python supports. Yet, many programmers never bother learning the powerful features that make this language object oriented.

The book teaches when and how OOP should be correctly applied. It emphasizes not only the simple syntax of OOP in Python, but also how to combine these objects into well-designed software.

This book will introduce you to the terminology of the object-oriented paradigm, focusing on object-oriented design with step-by-step examples. It will take you from simple inheritance, one of the most useful tools in the object-oriented programmer's toolbox, all the way through to cooperative inheritance, one of the most complicated. You will be able to raise, handle, define, and manipulate exceptions.

You will be able to integrate the object-oriented and the not-so-object-oriented aspects of Python. You will also be able to create maintainable applications by studying higher level design patterns. You'll learn the complexities of string and file manipulation, and how Python distinguishes between binary and textual data. Not one, but two very powerful automated testing systems will be introduced to you. You'll understand the joy of unit testing and just how easy they are to create. You'll even study higher level libraries such as database connectors and GUI toolkits and how they apply object-oriented principles.

Harness the power of Python 3 objects; it's not just a scripting language

Approach

The book begins with the very foundations of OOP and then uses practical examples to show how to correctly implement Object Oriented Programming in Python. Many examples are taken from real-world projects. The book focuses on high-level design as well as the gritty details of the Python syntax. The provided exercises inspire the reader to think about his or her own code, rather than providing solved problems.

Who this book is for

If you're new to Object Oriented Programming techniques, or if you have basic Python skills and wish to learn in depth how and when to correctly apply Object Oriented Programming in Python, this is the book for you.

If you are an object-oriented programmer for other languages, you too will find this book a useful introduction to Python, as it uses terminology you are already familiar with.

Python 2 programmers seeking a leg up in the new world of Python 3 will also find the book beneficial, and you need not necessarily know Python 2.

Python 3 Object Oriented Programming

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Table of Contents

Python 3 Object Oriented Programming

Credits

About the Author

About the Reviewers

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Errata

Piracy

Questions

1. Object-oriented Design

Object-oriented?

Objects and classes

Specifying attributes and behaviors

Data describes objects

Behaviors are actions

Hiding details and creating the public interface

Composition and inheritance

Inheritance

Inheritance provides abstraction

Multiple inheritance

Case study

Exercises

Summary

2. Objects in Python

Creating Python classes

Adding attributes

Making it do something

Initializing the object

Explaining yourself

Modules and packages

Organizing the modules

Absolute imports

Relative imports

Who can access my data?

Case study

Exercises

Summary

3. When Objects are Alike

Basic inheritance

Extending built-ins

Overriding and super

Multiple inheritance

The diamond problem

Different sets of arguments

Polymorphism

Case study

Exercises

Summary

4. Expecting the Unexpected

Raising exceptions

Raising an exception

What happens when an exception occurs?

Handling exceptions

Exception hierarchy

Defining our own exceptions

Exceptions aren't exceptional

Case study

Exercises

Summary

5. When to Use Object-oriented Programming

Treat objects as objects

Using properties to add behavior to class data

How it works

Decorators: another way to create properties

When should we use properties?

Managing objects

Removing duplicate code

In practice

Or we can use composition

Case study

Exercises

Summary

6. Python Data Structures

Empty objects

Tuples and named tuples

Named tuples

Dictionaries

When should we use dictionaries?

Using defaultdict

Lists

Sorting lists

Sets

Extending built-ins

Case study

Exercises

Summary

7. Python Object-oriented Shortcuts

Python built-in functions

Len

Reversed

Enumerate

Zip

Other functions

Comprehensions

List comprehensions

Set and dictionary comprehensions

Generator expressions

Generators

An alternative to method overloading

Default arguments

Variable argument lists

Unpacking arguments

Functions are objects too

Using functions as attributes

Callable objects

Case study

Exercises

Summary

8. Python Design Patterns I

Design patterns

Decorator pattern

Decorator example

Decorators in Python

Observer pattern

Observer example

Strategy pattern

Strategy example

Strategy in Python

State pattern

State example

State versus strategy

Singleton pattern

Singleton implementation

Module variables can mimic singletons

Template pattern

Template example

Exercises

Summary

9. Python Design Patterns II

Adapter pattern

Facade pattern

Flyweight pattern

Command pattern

Abstract factory pattern

Composite pattern

Exercises

Summary

10. Files and Strings

Strings

String manipulation

String formatting

Escaping braces

Keyword arguments

Container lookups

Object lookups

Making it look right

Strings are Unicode

Converting bytes to text

Converting text to bytes

Mutable byte strings

File IO

Placing it in context

Faking files

Storing objects

Customizing pickles

Serializing web objects

Exercises

Summary

11. Testing Object-oriented Programs

Why test?

Test-driven development

Unit testing

Assertion methods

Additional assertion methods in Python 3.1

Reducing boilerplate and cleaning up

Organizing and running tests

Ignoring broken tests

Testing with py.test

One way to do setup and cleanup

A completely different way to set up variables

Test skipping with py.test

py.test extras

How much testing is enough?

Case Study

Implementing it

Exercises

Summary

12. Common Python 3 Libraries

Database access

Introducing SQLAlchemy

Adding and querying objects

SQL Expression Language

Pretty user interfaces

TkInter

PyQt

Choosing a GUI toolkit

XML

ElementTree

Constructing XML documents

lxml

CherryPy

A full web stack?

Jinja Templating

The CherryPy blog web application

Exercises

Summary

Index

Python 3 Object Oriented Programming

Copyright © 2010 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 nor Packt Publishing, and its dealers and 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 of 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: July 2010

Production Reference: 1160710

Published by Packt Publishing Ltd.

32 Lincoln Road

Olton

Birmingham, B27 6PA, UK.

ISBN 978-1-849511-26-1

www.packtpub.com

Cover Image by Asher Wishkerman (<[email protected]>)

Credits

Author

Dusty Phillips

Reviewers

Jason Chu

Michael Driscoll

Dan McGee

Lawrence Oluyede

Acquisition Editor

Steven Wilding

Development Editor

Mayuri Kokate

Technical Editor

Vanjeet D'souza

Indexer

Hemangini Bari

Editorial Team Leader

Mithun Sehgal

Project Team Leader

Lata Basantani

Project Coordinator

Jovita Pinto

Proofreader

Chris Smith

Graphics

Geetanjali Sawant

Production Coordinator

Shantanu Zagade

Cover Work

Shantanu Zagade

About the Author

Dusty Phillips is a Canadian freelance software developer, teacher, martial artist, and open source aficionado. He is closely affiliated with the Arch Linux community and other open source projects. He maintains the Arch Linux storefronts, and compiled the popular Arch Linux Handbook. Dusty holds a Master's degree in Computer Science specializing in Human-Computer Interaction. He currently has six different Python interpreters installed on his computer.

I would like to thank my editors, Steven Wilding and Mayuri Kokate for well-timed encouragement and feedback. Many thanks to friend and mentor Jason Chu for getting me started in Python and for patiently answering numerous questions on Python, GIT, and life over the years. Thanks to my father, C. C. Phillips, for inspiring me to write while editing his terrific works of fiction. Finally, thanks to every person who has said they can't wait to buy my book; your enthusiasm has been a huge motivational force.

About the Reviewers

Jason Chu is the CTO and part founder of Oprius Software Inc. He's developed software professionally for over 8 years. Chu started using Python in 2003 with version 2.2. When not developing personal or professional software, he spends his time teaching karate, playing go, and having fun in his hometown: Victoria, BC, Canada. You'll often find him out drinking the Back Hand of God Stout at Christie's Carriage House.

Michael Driscoll has been programming Python for almost 4 years and has dabbled in other languages since the late nineties. He graduated from university with a Bachelor's degree in Science, majoring in Management Information Systems. Michael enjoys programming for fun and profit. His hobbies include biblical apologetics, blogging about Python at http://www.blog.pythonlibrary.org/, and learning photography. Michael currently works for the local government where he programs with Python as much as possible. This is his first book as a technical reviewer.

I would like to thank my mom without whom I never would have grown to love learning as much as I do. I would also like to thank Scott Williams for forcing me to learn Python as, without him, I wouldn't have ...

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