Design patterns are among the most powerful methods of building large software systems. With an increasing focus on optimized software architecture and design, it is important that software architects think about optimizations in object creation, code structure, and interaction between objects at the architecture or design level. This makes sure that the cost of software maintenance is low, and code can be easily reused and is adaptable to change. Moreover, providing frameworks for reusability and separation of concerns is key to software development today.
Chapter 1, Introduction to Design Patterns, goes through the basics of object-oriented programming and discusses object-oriented design principles in detail. This chapter gives a brief introduction to the concept of design patterns so that you will be able to appreciate the context and application of design patterns in software development.
Chapter 2, The Singleton Design Pattern, covers one of the simplest and well-known Creational design patterns used in application development—the Singleton design pattern. The different ways in which we can create a Singleton pattern in Python are also covered in this chapter along with examples. This chapter also covers the Monostate (or Borg) design pattern, which is a variant of the Singleton design pattern.
Chapter 3, The Factory Pattern – Building Factories to Create Objects, discusses another creational pattern, the Factory pattern. You will also learn about the Factory Method pattern and Abstract Factory pattern with a UML diagram, real-world scenarios, and Python v3.5 implementations.
Chapter 4, The Façade Pattern – Being Adaptive with Façade, shows you another type of design pattern, the Structural design pattern. We will be introduced to the concept of Façade and learn how it is applicable to software design with the help of the Façade design pattern. You'll also learn its implementation with a sample Python application using a real-world scenario.
Chapter 5, The Proxy Pattern – Controlling Object Access, deals with the Proxy pattern that falls into the category of Structural design patterns. We will be introduced to the Proxy as a concept and discuss the design pattern and see how it is used in software application development. You'll also learn about the different variants of the Proxy pattern—Virtual Proxy, Smart Proxy, Remote Proxy, and Protective Proxy.
Chapter 6, The Observer Pattern – Keeping Objects in the Know, talks about the third type of design pattern—the behavioral design pattern. We will be introduced to the Observer design pattern with examples. In this chapter, you'll learn how to implement the Push and Pull models of the Observer pattern and the principles of loose coupling. We'll also see how this pattern is critical when it comes to applying it to cloud applications and distributed systems.
Chapter 7, The Command Pattern – Encapsulating Invocation, tells you about the Command design pattern. We will be introduced to the Command design pattern and discuss how it is used in software application development with a real-world scenario and Python implementation. We will also study two main aspects of the Command pattern—an implementation of redo/rollback operations and asynchronous task execution.
Chapter 8, The Template Method Pattern – Encapsulating Algorithm, discusses the Template design pattern. Like the Command pattern, the Template pattern falls into the category of Behavioral patterns. Here, we discuss the Template method pattern, and you will learn about Hooks with an implementation. We'll also cover the Hollywood principle that helps us appreciate this pattern better.
Chapter 9, Model-View-Controller – Compound Patterns, talks about Compound patterns. We will be introduced to the Model-View-Controller design pattern and discuss how it is used in software application development. MVC is easily one of the most used design patterns; in fact, many Python frameworks are based on this principle. You will learn about the details of MVC implementation with an example application written in Python Tornado (a framework used by Facebook).
Chapter 10, The State Design Pattern, introduces you to the State design pattern, which falls into the category of Behavioral patterns just like the Command or Template design patterns. We will discuss how it is used in software application development.
Chapter 11, AntiPatterns, tells you about AntiPatterns—what we shouldn't do as architects or software engineers.
All you need is Python v3.5, and you can download it from https://www.python.org/downloads/.
This book is for Python developers and software architects who care about software design principles and details of application development aspects in Python. It requires a basic understanding of programming concepts and beginner-level Python development experience. It will also be helpful for students and teachers in live learning environments.
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "The Car object will have attributes such as fuel level, isSedan, speed, and steering wheel and coordinates."
A block of code is set as follows:
class Person(object):
def __init__(self, name, age): #constructor
self.name = name #data members/ attributes
self.age = age
def get_person(self,): # member function
return "<Person (%s, %s)>" % (self.name, self.age)
p = Person("John", 32) # p is an object of type Person
print("Type of Object:", type(p), "Memory Address:", id(p))New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "In Python, the concept of encapsulation (data and method hiding) is not implicit, as it doesn't have keywords such as public, private, and protected (in languages such as C++ or Java) that are required to support encapsulation."
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