Alex Popescu wrote:
Alex Popescu <no*****************@gmail.comwrote in
news:Xn**************************@80.91.229.5:
>"Diez B. Roggisch" <de***@nospam.web.dewrote in
news:5g*************@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
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
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC/Ltd
http://www.holdenweb.com
Skype: holdenweb
http://del.icio.us/steve.holden
--------------- Asciimercial ------------------
Get on the web: Blog, lens and tag the Internet
Many services currently offer free registration
----------- Thank You for Reading -------------
