Python Design Pattern

Introduction

• A practice project for Gang of Four design patterns.

Creational Design Pattern

The design patterns that deal with the creation of an object.

• Singleton Pattern
  • Purpose: ensure that no more than a single instance of a class exists.
  • When to use: when you want to control access to a shared resource.
  • Examples: Loggers, caching, thread pools, database connection, configuration access, ...
• Factory Method Pattern
  • Purpose: allow a class to defer instantiation to its subclasses.
  • When to use:
    • when a caller can't anticipate the type of objects it must create.
    • when you have many objects of a common type.
  • Examples: strategy design pattern, object pool (facilitate caching)
• Builder Pattern
  • Purpose: encapsulate reusable logic of building complex logic.
  • When to use:
    • when you have a complex class with many constructors.
    • when you have to build complex composite tree objects.
  • Examples: document readers

Structural Design Pattern

The design patterns in this category deal with the class structure such as Inheritance and Composition.

• Adapter Pattern
  • Purpose: convert the interface contract of one class to be compatible with another
  • When to use: when you have an existing class or contract that you would like to reuse but its interface isn't compatible with the rest of your code.
  • Examples: XML to JSON adapter

Behavioral Design Pattern

This type of design pattern provides solutions for better interaction between objects, how to provide loose coupling, and flexibility to extend easily in the future.

• Strategy Pattern
  • Purpose: extract related algorithms (or any piece of code) into separate classes and define a common interface for them.
  • When to use: when you want to abstract the business logic of a class from its implementation details.
  • Examples: discount handlers
• Observer Pattern
• State Pattern