python单例模式的实现

1 线程不安全的单例模式

 # -*- 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)

2 线程安全的单例模式

 # -*- 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)