Singleton Design Pattern Implementation in Python

Design Pattern: Singleton Design Pattern

Problem Analysis:

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

Code Template - Singleton Design Pattern Implementation (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(id(instance1) == id(instance2))  # Output: True

Implementation Details:

1. Singleton Class: Defines a metaclass Singleton that tracks instances of its subclasses using a dictionary _instances.
2. call Method: Overrides the __call__ method to ensure only one instance of each class is created and returned.
3. MyClass Definition: Inherits from Singleton metaclass to enforce the Singleton pattern.
4. Instance Creation: instance1 and instance2 are instances of MyClass.
5. Instance Comparison: print(id(instance1) == id(instance2)) compares the identities of two instances, returning True if they are the same instance.

Code Explanation:

• The Singleton design pattern restricts the instantiation of a class to a single instance and provides a way to access that instance globally.
• The metaclass Singleton keeps track of instances for each class and ensures that only one instance is created.
• By using the metaclass Singleton, the class MyClass becomes a Singleton class with only one instance created.