I'm learning Python and i've been trying to implement a Singleton-type class as a test. The code i have is as follows:

_Singleton__instance = Noneclass Singleton:def __init__(self):global __instanceif __instance == None:           self.name = "The one"__instance = selfelse:self = __instance

This works in part but the self = __instance part seems to be failing. I've included some output from the interpretor to demonstrate (the code above is saved in singleton.py):

>>> import singleton
>>> x = singleton.Singleton()
>>> x.name
'The one'
>>> singleton._Singleton__instance.name
'The one'
>>> y = singleton.Singleton()
>>> y.name
Traceback (most recent call last):File "<stdin>", line 1, in <module>
AttributeError: Singleton instance has no attribute 'name'
>>> type(y)
<type 'instance'>
>>> dir(y)
['__doc__', '__init__', '__module__']

Is it possible to do what i'm trying? If not is there another way of doing this?

Any suggestions welcome.

Cheers.

Assigning to an argument or any other local variable (barename) cannot ever, possibly have ANY effect outside the function; that applies to your self = whatever as it would to ANY other assignment to a (barename) argument or other local variable.

Rather, override __new__:

class Singleton(object):__instance = Nonedef __new__(cls):if cls.__instance == None:cls.__instance = object.__new__(cls)cls.__instance.name = "The one"return cls.__instance

I've done other enhancements here, such as uprooting the global, the old-style class, etc.

MUCH better is to use Borg (aka monostate) instead of your chosen Highlander (aka singleton), but that's a different issue from the one you're asking about;-).