python单例模式的实现

 # -*- coding:utf-8 -*-

 from __future__ import unicode_literals

 import functools

 def singleton(func):

     """线程不安全的单例模式"""

     @functools.wraps(func)

     def wrapper(*args, **kw):

         if not hasattr(func, 'singleton_attr'):

             func.singleton_attr = func(*args, **kw)

         return func.singleton_attr

     return wrapper

 if __name__ == '__main__':

     @singleton

     def get_demo_list():

         return [1, 2, 3]

     list_1 = get_demo_list()

     list_2 = get_demo_list()

     assert id(list_1) == id(list_2)

 # -*- coding:utf-8 -*-

 from __future__ import unicode_literals

 import threading

 class SingletonMixin(object):

     """

     thread safe singleton base class

     refer: https://gist.github.com/werediver/4396488

     # Based on tornado.ioloop.IOLoop.instance() approach.

     # See https://github.com/facebook/tornado

     """

     __singleton_lock = threading.Lock()

     __singleton_instance = None

     @classmethod

     def instance(cls):

         """

         :rtype: SingletonMixin

         """

         if not cls.__singleton_instance:

             with cls.__singleton_lock:

                 if not cls.__singleton_instance:

                     cls.__singleton_instance = cls()

         return cls.__singleton_instance

 class SingleDemo(SingletonMixin):

     def __init__(self):

         pass

     @classmethod

     def instance(cls):

         """

         :rtype: SingleDemo

         """

         return super(SingleDemo, cls).instance()

 if __name__ == '__main__':

     obj_1 = SingleDemo.instance()

     obj_2 = SingleDemo.instance()

     assert id(obj_1) == id(obj_2)