In python, most of us use the Borg Singleton like, which is not a true Singleton, since only the ‘state is shared’. In fact, you use distinct objects but they share the same __dict__.

Yesterday, i played a bit w/ python metaclass. Beside this can be really usefull under certain condition, i discover that you can build a Borg with that too :)

class Single_imp:
def __init__(cls,name,base,dict):
cls.value = 1
def __call__(cls):
return cls
def setValue(cls,value):
cls.value = value

class Single:
__metaclass__ = Single_imp

a = Single()
b = Single()
print a
print b
a.setValue(10)
print b.value

and the result:

<__main__.Single_imp instance at 0x401eb96c>
<__main__.Single_imp instance at 0x401eb96c>
10

Ok .. the code looks strange.. and not a true Singleton .. but how can i build a real true in Python ?