singleton.py

#coding:utf-8

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

class MyClass(Singleton):
    a = 1

#共享属性
class Borg(object):
    _state = {}
    def __new__(cls, *args, **kw):
        ob = super(Borg, cls).__new__(cls, *args, **kw)
        ob.__dict__ = cls._state
        return ob
 
class MyClass2(Borg):
    a = 1
#装饰器版本
def singleton(cls, *args, **kw):
    instances = {}
    def getinstance():
        if cls not in instances:
            instances[cls] = cls(*args, **kw)
        return instances[cls]
    return getinstance

@singleton
class MyClass:
  ...
# import方法
# mysingleton.py
class My_Singleton(object):
    def foo(self):
        pass

my_singleton = My_Singleton()

# to use
from mysingleton import my_singleton

my_singleton.foo()