实现单例模式(python)

2015-03-18 22:12 编程相关 python , 设计模式

实现单例模式(python)

目录

方法一：重写__new__方法二：使用装饰器方法三：使用元类

方法一：重写new


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class Singleton(object):
    def __new__(cls, *args, **wargs):
        if not hasattr(cls, "_instance"):
            cls._instance = super(Singleton, cls).__new__(cls, *args, **wargs)
        return cls._instance

方法二：使用装饰器


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def decorate(cls):
    _instances = {}
    def _getInstance(*args, **kwargs):
        if cls not in _instances:
            _instances[cls] = cls(*args, **kwargs)
        return _instances[cls]
    return _getInstance
@decorate
class Singleton(object):
    pass

方法三：使用元类


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class SingletonMeta(type):
    _instances = {}
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(SingletonMeta, cls).__call__(*args, **kwargs)
        return cls._instances[cls]
# for python3
class Singleton(metaclass=SingletonMeta):
    pass
# for python2
class Singleton(object):
    __metaclass__ = SingletonMeta

想要了解元类更多内容，请前往Python元类(metaclass)及其用途