#coding:utf-8
‘‘‘
单例实现之装饰器实现‘‘‘
def singleton(cls, *args, **kwargs):
    instance = {}
    def _singleton():
        if cls not in instance:
            instance[cls] = cls(*args, **kwargs)
        return instance
    return _singleton

@singleton
def MyClass():
    a = 1
    def __init__(self, x=0):
        self.x = x

a = MyClass()
b = MyClass()

a.a = 3
print b.a
#3
a is b
#True