Python 实现单例模式

一、借助 __new__ 来实现

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

    def __init__(self, x):
        self.x = x

a = Singleton(1)
b = Singleton(2)
print a==b
print a.x, b.x
#True
#2 2

二、借助类属性与get函数

class Myclass(object):
    _sigle_cls = None
    def __init__(self, x):
        self.x = x
    @classmethod
    def get_cls(cls, *args, **argk):
        if not cls._sigle_cls:
            cls._sigle_cls = cls(*args, **argk)
        return cls._sigle_cls

a = Myclass.get_cls(1)
print a.x
b = Myclass.get_cls(2)
print "a.x:",a.x, "b.x", b.x

#a.x: 1 b.x 1

这两种方式还是有区别的，不知道看了此博文的同学发现了没？