singleton ... again

Ethan Furman ethan at
Thu Feb 13 19:31:12 CET 2014

On 02/13/2014 09:57 AM, Roy Smith wrote:
> In article <mailman.6850.1392313443.18130.python-list at>,
>   Ethan Furman <ethan at> wrote:
>> Say you have a class that represents serial ports or your computer.  You
>> should get the same object every time you ask
>> for SerialPort(2).
> Why?  Certainly, you should get objects which refer to the same physical
> port.  So:
> port_a = SerialPort(2)
> port_b = SerialPort(2)
> port_a.enable()
> assert port_b.is_shutdown() == False
> port_a.shutdown()
> assert port_b.is_shutdown() == True
> But, why do they have to be the same object?  Why should I care if
> port_a is port_b
> is False, as long as all operations I perform on either are reflected in
> correct state changes on the other one?

You mean use the Borg pattern instead of the Singleton pattern?  As far as I can tell they are two shades of the same 
thing.  Are there any drastic differences between the two?  Besides one having many instances that share one __dict__ 
and the other just having one instance and one __dict__?


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