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Learning Python Design Patterns - Second Edition

You're reading from   Learning Python Design Patterns - Second Edition

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Product type Paperback
Published in Feb 2016
Publisher
ISBN-13 9781785888038
Length 164 pages
Edition 2nd Edition
Languages
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Authors (2):
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Gennadiy Zlobin Gennadiy Zlobin
Author Profile Icon Gennadiy Zlobin
Gennadiy Zlobin
Chetan Giridhar Chetan Giridhar
Author Profile Icon Chetan Giridhar
Chetan Giridhar
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Toc

Table of Contents (13) Chapters Close

Preface 1. Introduction to Design Patterns 2. The Singleton Design Pattern FREE CHAPTER 3. The Factory Pattern – Building Factories to Create Objects 4. The Façade Pattern – Being Adaptive with Façade 5. The Proxy Pattern – Controlling Object Access 6. The Observer Pattern – Keeping Objects in the Know 7. The Command Pattern – Encapsulating Invocation 8. The Template Method Pattern – Encapsulating Algorithm 9. Model-View-Controller – Compound Patterns 10. The State Design Pattern 11. AntiPatterns Index

Lazy instantiation in the Singleton pattern

One of the use cases for the Singleton pattern is lazy instantiation. For example, in the case of module imports, we may accidently create an object even when it's not needed. Lazy instantiation makes sure that the object gets created when it's actually needed. Consider lazy instantiation as the way to work with reduced resources and create them only when needed.

In the following code example, when we say s=Singleton(), it calls the __init__ method but no new object gets created. However, actual object creation happens when we call Singleton.getInstance(). This is how lazy instantiation is achieved.

class Singleton:
    __instance = None
    def __init__(self):
        if not Singleton.__instance:
            print(" __init__ method called..")
        else:
            print("Instance already created:", self.getInstance())
    @classmethod
    def getInstance(cls):
        if not cls.__instance:
            cls.__instance...
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Learning Python Design Patterns - Second Edition - Second Edition
Published in: Feb 2016
Publisher:
ISBN-13: 9781785888038
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