python 实现单例模式的四种方法

1、__new__

class Borg(object):    def __new__(cls, *args, **kwargs):        if not hasattr(cls, '_instance'):            ob = super(Borg, cls)            cls._instance = ob.__new__(cls, *args, **kwargs)        return cls._instance

class MyClass(Borg):    def __init__(self):        self.a = 1

if __name__ == '__main__':    a1 = MyClass()    a2 = MyClass()    a1.a = 10    print(a1.a)    print(a2.a)    print(a1.__dict__)

输出：

1010{'a': 10}

2、共享属性

class Borg2(object):    _state = {}    def __new__(cls, *args, **kwargs):        ob = super(Borg2, cls).__new__(cls, *args, **kwargs)        ob.__dict__ = cls._state        return ob

class MyClass(Borg2):    def __init__(self):        self.a = 1

if __name__ == '__main__':    a1 = MyClass()    a2 = MyClass()    a1.a = 10    print(a1.a)    print(a2.a)    print(a1.__dict__)

输出：

1010{'a': 10}

3、装饰器

def singleton(cls, *args, **kwargs):    instances = {}    def getinstance():        if cls not in instances:            instances[cls] = cls(*args, **kwargs)        return instances[cls]    return getinstance

@singletonclass MyClass(object):    def __init__(self):        self.a = 1

if __name__ == '__main__':    a1 = MyClass()    a2 = MyClass()    a1.a = 10    print(a1.a)    print(a2.a)    print(a1.__dict__)

输出：

1010{'a': 10}

4、import方法

# mysingleton .pyclass MyClass(object):    def __init__(self):        self.a = 1s_myclass = MyClass()

# to usefrom mysingleton import s_myclasss_myclass.a