Singleton Design Pattern in Python

Design Pattern: Singleton

Problem Analysis

• The provided code shows the implementation of a Singleton design pattern in Python.
• The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance.

Code Template: Singleton Design Pattern in Python

class Singleton(type):
    _instances = {}
    
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instances[cls]

class MyClass(metaclass=Singleton):
    pass

instance1 = MyClass()
instance2 = MyClass()

print(instance1 == instance2)  # Output should be True

Implementation Details:

• The Singleton class uses a dictionary _instances to store created instances of classes.
• The __call__ method is overridden to check if the class instance exists in _instances dictionary; if not, it creates a new instance.
• The metaclass=Singleton statement in MyClass declaration ensures that only one instance of MyClass is created.

Benefits:

• Guarantees a single instance of a class throughout the application.
• Provides a global access point to that instance.
• Lazy initialization allows instance creation only when needed.

Conclusion

The Singleton design pattern ensures that only one instance of a class exists at any given time, providing a way to access that instance globally. The template showcases a clean and concise implementation of the Singleton pattern in Python, demonstrating its usefulness in scenarios requiring a single shared instance.