python singleton

fenghzy

方法一：用元类的方式实现一个singleton。



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
方法二：用修饰类的方式实现一个Singleton。



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