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Mastering Object-Oriented Python

You're reading from   Mastering Object-Oriented Python Build powerful applications with reusable code using OOP design patterns and Python 3.7

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Product type Paperback
Published in Jun 2019
Publisher Packt
ISBN-13 9781789531367
Length 770 pages
Edition 2nd Edition
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Author (1):
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Steven F. Lott Steven F. Lott
Author Profile Icon Steven F. Lott
Steven F. Lott
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Table of Contents (25) Chapters Close

Preface
Who this book is for
What this book covers
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1. Preliminaries, Tools, and Techniques FREE CHAPTER 2. The __init__() Method 3. Integrating Seamlessly - Basic Special Methods 4. Attribute Access, Properties, and Descriptors 5. The ABCs of Consistent Design 6. Using Callables and Contexts 7. Creating Containers and Collections 8. Creating Numbers 9. Decorators and Mixins - Cross-Cutting Aspects 10. Serializing and Saving - JSON, YAML, Pickle, CSV, and XML 11. Storing and Retrieving Objects via Shelve 12. Storing and Retrieving Objects via SQLite 13. Transmitting and Sharing Objects 14. Configuration Files and Persistence 15. Design Principles and Patterns 16. The Logging and Warning Modules 17. Designing for Testability 18. Coping with the Command Line 19. Module and Package Design 20. Quality and Documentation

The Python runtime and special methods

One of the essential concepts for mastering object-oriented Python is to understand how object methods are implemented. Let's look at a relatively simple Python interaction:

>>> f = [1, 1, 2, 3]
>>> f += [f[-1] + f[-2]]
>>> f
[1, 1, 2, 3, 5]

We've created a list, f, with a sequence of values. We then mutated this list using the += operator to append a new value. The f[-1] + f[-2] expression computes the new value to be appended.

The value of f[-1] is implemented using the list object's __getitem__() method. This is a core pattern of Python: the simple operator-like syntax is implemented by special methods. The special methods have names surrounded with __ to make them distinctive. For simple prefix and suffix syntax, the object is obvious; f[-1] is implemented as f.__getitem__(-1).

The additional operation is similarly implemented by the __add__() special method. In the case of a binary operator, Python will try both operands to see which one offers the special method. In this example, both operands are integers, and both will provide a suitable implementation. In the case of mixed types, the implementation of the binary operator may coerce one value into another type. f[-1] + f[-2], then, is implemented as f.__getitem__(-1).__add__(f.__getitem__(-2)).

The update of f by the += operator is implemented by the __iadd__() special method. Consequently, f += [x] is implemented as f.__iadd__([x]).

Throughout the first eight chapters, we'll look very closely at these special methods and how we can design our classes to integrate very tightly with Python's built-in language features. Mastering the special methods is the essence of mastering object-oriented Python.

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Mastering Object-Oriented Python - Second Edition
Published in: Jun 2019
Publisher: Packt
ISBN-13: 9781789531367
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