Python Implementation of the Singleton Design Pattern

singleton.py

class Singleton(type):
    def __init__(cls, *args, **kwargs):
        # When creating the class object (class ClassName), set the shared instance variable.
        super(Singleton, cls).__new__(*args, **kwargs)
        cls.__instance = None

    def __call__(cls, *args, **kwargs):
        # When instanciating (obj = ClassName()), return shared instance (or create it if 1st time).
        if cls.__instance is None:
            cls.__instance = super(Singleton, cls).__call__(*args, **kwargs)
        return cls.__instance