| class Singleton(type): | |
| """ | |
| Define an Instance operation that lets clients access its unique | |
| instance. | |
| """ | |
| 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 MyClass(metaclass=Singleton): | |
| """ | |
| Example class. | |
| """ | |
| pass | |
| # class Singleton(object): | |
| # _instance = None | |
| # def __new__(cls, *args, **kwargs): | |
| # if not isinstance(cls._instance, cls): | |
| # print("Constructing singleton for", cls, 'with parameters', args, kwargs) | |
| # # cls._instance = object.__new__(cls, *args, **kwargs) | |
| # cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs) | |
| # return cls._instance | |
| # class Singleton(object): | |
| # _instance = None | |
| # def __new__(cls, *args, **kwargs): | |
| # if not isinstance(cls._instance, cls): | |
| # cls._instance = object.__new__(cls, *args, **kwargs) | |
| # return cls._instance | |