单例模式

singleton.py

# Method-1
class Foo(object):
    __instance = None
    def __new__(cls, *args, **kwargs):
        if Foo.__instance is None:
            Foo.__instance = object.__new__(cls, *args, **kwargs)
        return Foo.__instance

a = Foo()
b = Foo()
print(a is b)


# Method-2
def singleton(cls, *args, **kw):  
    instances = {}  
    def _singleton():  
        if cls not in instances:  
            instances[cls] = cls(*args, **kw)  
        return instances[cls]  
    return _singleton

@singleton
class Woo(object):
    pass

c = Woo()
d = Woo()
print(c is d)