Singleton is a creational design pattern, which is intended to be used when a class must have exactly one instance, no more, no less.
Let’s create a singleton Logger class that will be responsible for logging different actions.
The most popular way of creating a singleton in Python is using the metaclass approach:
A metaclass is the class of a class. Like a class defines how an instance of the class behaves, a metaclass defines how a class behaves. A class is an instance of a metaclass.
Let’s get to the code:
class Singleton(type): def __init__(cls, name, bases, attrs, **kwargs): super().__init__(name, bases, attrs) cls._instance = None def __call__(cls, *args, **kwargs): if cls._instance is None: cls._instance = super().__call__(*args, **kwargs) return cls._instance class Logger(metaclass=Singleton): #some class pass l1 = Logger() l2 = Logger() print(l1 is l2)