liuxiaoyan@development:~/mysite$ cat Singleton.py

class Singleton(type):

        """Singleton Metaclass"""

        def __init__(cls, name, bases, dic):

                super(Singleton, cls).__init__(name, bases, dic)

                cls.instance = None

        def __call__(cls, *args, **kwargs):

                if cls.instance is None:

                        cls.instance = super(Singleton, cls).__call__(*args, **kwargs)

                return cls.instance

class MyClass(object):

        __metaclass__ = Singleton  

        def __init__(self,arg):

                self.arg = arg  

myClass1=MyClass("myClass1")

myClass2=MyClass("myClass2")

print myClass1 is myClass2

liuxiaoyan@development:~/mysite$ python Singleton.py

True

liuxiaoyan@development:~/mysite$ cat Singleton.py

class Singleton:

    def __init__( self, decorated ):

        self._decorated = decorated

    def Instance( self ):

        try:

            return self._instance

        except AttributeError:

            self._instance = self._decorated

            return self._instance  

    def __call__( self ):

        raise TypeError( 'single instance allowed' )  

@Singleton

class MyClass:

    def __init__( self ):

        print( 'created' )

#myClass=MyClass()  #不能再用这种方式创建MyClass实例，会产生异常

#用以下方法创建实例

myClass1=MyClass.Instance()

myClass2=MyClass.Instance()

print myClass1 is myClass2

print id(myClass1)

print id(myClass2)

liuxiaoyan@development:~/mysite$ python Singleton.py

True

140716352778528

140716352778528