标签：decorator 高级 new tor python 相同 one 单利 str
方法一
实现__new__方法，然后将类的一个实例绑定到类变量_instance上；如果cls._instance为None，则说明该类还没有被实例化过，new一个该类的实例，并返回；如果cls._instance不为None，直接返回_instance，代码如下
class Singleton(object): def __new__(cls, *args, **kwargs): if not hasattr(cls, ‘_instance‘): orig = super(Singleton, cls) cls._instance = orig.__new__(cls, *args, **kwargs) return cls._instance class MyClass(Singleton): a = 1 one = MyClass() two = MyClass() #one和two完全相同,可以用id(), ==, is检测 print id(one) # 29097904 print id(two) # 29097904 print one == two # True print one is two # True
方法二
本质上是方法一的升级版，使用__metaclass__（元类）的高级python用法，具体代码如下：
class Singleton2(type): def __init__(cls, name, bases, dict): super(Singleton2, cls).__init__(name, bases, dict) cls._instance = None def __call__(cls, *args, **kwargs): if cls._instance is None: cls._instance = super(Singleton2, cls).__call__(*args, **kwargs) return cls._instance class MyClass2(object): __metaclass__ = Singleton2 a = 1 one = MyClass2() two = MyClass2() print id(one) # 31495472 print id(two) # 31495472 print one == two # True print one is two # True
方法三
使用Python的装饰器(decorator)实现单例模式，这是一种更Pythonic的方法；单利类本身的代码不是单例的，通装饰器使其单例化，代码如下：
def singleton(cls, *args, **kwargs): instances = {} def _singleton(): if cls not in instances: instances[cls] = cls(*args, **kwargs) return instances[cls] return _singleton @singleton class MyClass3(object): a = 1 one = MyClass3() two = MyClass3() print id(one) # 29660784 print id(two) # 29660784 print one == two # True print one is two # True
标签：decorator 高级 new tor python 相同 one 单利 str
原文地址：http://www.cnblogs.com/yunfeiqi/p/6840325.html
