Patterns in Python – Creational

In this section, we will take a look at a few of the common creational patterns. We will start with Singleton, and then go on to Prototype, Builder, and Factory, in that order.

The Singleton pattern

The Singleton pattern is one of the most well-known and easily understood patterns in the entire pantheon of design patterns. It is usually defined as:

A Singleton is a class which has only one instance and a well-defined point of access to it.

The requirements of a Singleton can be summarized as follows:

• A class must have only one instance accessible via a well-known access point

• The class must be extensible by inheritance without breaking the pattern

• The simplest Singleton implementation in Python is shown next. It is done by overriding the __new__ method of the base object type:

  # singleton.py
  class Singleton(object):
      """ Singleton in Python """
      
      _instance = None
      
      def __new__(cls):
          if cls._instance == None:
              cls._instance = object...