Singleton in Python Cookbook
nospam.themindstorm at gmail.com
Thu Jul 26 01:23:46 CEST 2007
Alex Popescu <nospam.themindstorm at gmail.com> wrote in
news:Xns9979172DC38F1themindstorm at 184.108.40.206:
> "Diez B. Roggisch" <deets at nospam.web.de> wrote in
> news:5gq00tF3fm71gU1 at mid.uni-berlin.de:
>> Alex Popescu schrieb:
>>> Hi all!
>>> I was reading through Python Cookbook the Singleton recipe. At this
>>> moment I am a bit puzzled as the example in the book is not working
>>> resulting in:
>>> TypeError: type.__new__(SingleSpam): SingleSpam is not a subtype of
>>> (I haven't presented the original code as I am not sure about
>> AFAIK the cookbook is completely found online at ASPN. So no sweat
>> publishing it here.
>> And regarding the problem: is it possible that you forgot to subclass
>> SingleSpam from object?
> The exact code:
> class Singleton(object):
> """ A Pythonic Singleton """
> def _ _new_ _(cls, *args, **kwargs):
> if '_inst' not in vars(cls):
> cls._inst = type._ _new_ _(cls, *args, **kwargs)
> return cls._inst
> if _ _name_ _ == '_ _main_ _':
> class SingleSpam(Singleton):
> def _ _init_ _(self, s): self.s = s
> def _ _str_ _(self): return self.s
> s1 = SingleSpam('spam')
> print id(s1), s1.spam( )
> s2 = SingleSpam('eggs')
> print id(s2), s2.spam( )
> .w( the_mindstorm )p.
I got it working in 2 ways:
""" A Pythonic Singleton """
def __new__(cls, *args, **kwargs):
if '_singletoninstance' not in vars(cls):
#variant 1: cls._singletoninstance = object.__new__(cls, *args,
#variant 2: cls._singletoninstance = super(type, cls).__new__(cls,
Both of these seem to work.
.w( the_mindstorm )p.
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