Implementation of a Python singleton pattern

In some cases we need a singleton pattern to reduce the waste of program resources, and the implementation of Singleton mode is also convenient in the Python language.

I now take the tornado framework of the implementation of the Ioloop class singleton mode, for example, interested can see the source of their own

1 classIoloop (configurable):2 ...3 4 @staticmethod5     definstance ():6         """Returns a global ' Ioloop ' instance.7 8 Most applications has a single, and the global ' Ioloop ' running on the9 main thread. use the This method to get the this instance fromTen another thread. To get the current thread ' s ' ioloop ', use ' current ' () '. One         """ A         if  notHasattr (Ioloop,"_instance"): - With Ioloop._instance_lock: -                 if  notHasattr (Ioloop,"_instance"): the                     #New instance after double check -Ioloop._instance =Ioloop () -         returnioloop._instance -  + @staticmethod -     definitialized (): +         """Returns True if the singleton instance has been created.""" A         returnHasattr (Ioloop,"_instance") at  -     defInstall (self): -         """installs this ' Ioloop ' object as the singleton instance. -  - This was normally not necessary as ' instance () ' would create - An ' ioloop ' in demand, but if you could want to call ' install ' to use in a custom subclass of ' Ioloop '. -         """ to         assert  notioloop.initialized () +Ioloop._instance = Self -  the @staticmethod *     defclear_instance (): $         """Clear the global ' Ioloop ' instance.Panax Notoginseng  - .. versionadded:: 4.0 the         """ +         ifHasattr (Ioloop,"_instance"): A             delIoloop._instance

Where the code that implements the singleton pattern is

if  not " _instance " ): With            ioloop._instance_lock:                ifnot"_instance"  ):                    #  New instance after double check                    ioloop._instance = Ioloop ( )        return ioloop._instance

And the method of guaranteeing the invocation of Singleton mode is very simple:

Tornado.ioloop.IOLoop.instance (). Start ()

The above-mentioned source code class in the remaining several methods are used in conjunction with the Singleton pattern, they implemented a single example of the function

Implementation of a Python singleton pattern