Implementing a Singleton in Pure Python

Learn how to implement the Singleton design pattern in pure Python to ensure only one instance of a class exists.

Implementing Singleton in Pure Python

The Singleton design pattern ensures a class has only one instance and provides a global point of access to it. This is useful when you want to control resources like database connections or configuration objects.

Why Use Singleton?

Singleton helps enforce a single shared state across your application. For example, you may need a central configuration object or a single logging instance.

Python Implementation

Unlike languages with private constructors, Python uses the __new__ method to control object creation.

Here’s how to create a Singleton class:

class Singleton:
    _instance = None

    def __new__(cls, *args, **kwargs):
        if not cls._instance:
            cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
        return cls._instance

# Test Singleton
s1 = Singleton()
s2 = Singleton()
print(s1 is s2)  # True

This ensures any new instantiation returns the same object.

Key Takeaways

By overriding __new__, you control object creation and enforce single instance behavior in Python. Singleton should be used judiciously as it introduces global state.

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