Twice instanciation

Michele Simionato mis6 at pitt.edu
Fri Jun 13 14:03:26 CEST 2003


Salvatore <artyprog at wanadoo.fr> wrote in message news:<bcakmg$jv7$1 at news-reader14.wanadoo.fr>...
> Hello,
> 
> Is it possible to avoid twice instanciation
> of the same variable ?
> 
> class Global:
>     def __init__(self,init=0):
>        self.value = init
> 
> g = Global() #instanciating one time ok
> g = Global() #instanciating two times would raise an exception
> 
> 
> Regards
> 
> Salvatore

You can do this:

class DoubleInstantiationError(Exception): pass

class Global:
    alreadyinstantiated=False
    def __init__(self,init=0):
        if self.__class__.alreadyinstantiated:
            raise DoubleInstantiationError()
        self.value = init
        self.__class__.alreadyinstantiated=True

g = Global() #instanciating one time ok
print g
g = Global() #instanciating two times would raise an exception

Notice that you would have an exception even using a different name
for 'g' the second time. You can alway subclass Global, anyway, if
you need another variable.
HTH,

                   Michele




                        Michele




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