Alex Popescu wrote:
> Alex Popescu <[EMAIL PROTECTED]> wrote in
> news:[EMAIL PROTECTED]:
>
>> "Diez B. Roggisch" <[EMAIL PROTECTED]> wrote in
>> news:[EMAIL PROTECTED]:
>>
>>> 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
>>>> type
>>>>
>>>> (I haven't presented the original code as I am not sure about
>>>> copyrights).
>>> 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?
>>>
>>> Diez
>> 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( )
>>
>> ./alex
>> --
>> .w( the_mindstorm )p.
>>
> I got it working in 2 ways:
>
> class Singleton(object):
> """ A Pythonic Singleton """
> def __new__(cls, *args, **kwargs):
> if '_singletoninstance' not in vars(cls):
> #variant 1: cls._singletoninstance = object.__new__(cls, *args,
> **kwargs)
> #variant 2: cls._singletoninstance = super(type, cls).__new__(cls,
> *args, **kwargs)
> return cls._singletoninstance
>
> Both of these seem to work.
>
If, that is, "work" means "Raise an AttributeError due to the missing
spam() method". This appears to fix that problem:
class Singleton(object):
""" A Pythonic Singleton """
def __new__(cls, *args, **kwargs):
if '_inst' not in vars(cls):
cls._inst = object.__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
s2 = SingleSpam('eggs')
print id(s2), s2
print str(s1)
regards
Steve
--
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