How to create a singleton in Python?
The singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance.
Using metaclass
In Python, there are multiple ways to do that but the most effective is using metaclasses.
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 Logger(metaclass=Singleton):
pass
In the example above, the Logger class is a singleton - every instance of the Logger will be the same. There will always be only one Logger and all Logger objects will refer to that one Logger.
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