[Tutor] Class variable & object variable

[Damien]

thx for your quick (and complete) answers.

to Alan G :
I will try to see what setattr() and getattr() can do for me. I'm not 
used to this stuff.

to Alex Nedelcu :
If I understand correctly :
There are two different references (A.d in the dict of the class A and 
z.d in the dict of the object z) but on the same object, am I right ?
(with z = A())

Alan G a écrit :

>> class A(object):
>>    d = 50
>>    def __init__(self):
>>       print "Hello"
>>
>> >>> z = A()
>> >>> A.d
>> 50
>> >>> z.d
>> 50
>> 1) Why ?? d is not an object variable but a class variable !!!
>
>
> Yes which means (definition of a class variable) that it's part of
> every class and instance of the class.
>
>> object z, d is not defined (in my mind, not for Python, as you can 
>> see)(it's the same in Java :  all static variables can be accessed 
>> from an object of the class or the class itself).
>
>
> Thats what class attributes do, they are part of the class and
> thus of instances of the class. After all, methods are defined at the
> class level too and if they were not available to the instance
> except by calling like:
>
> A.f(z)
>
> it would get very tiresome.
>
>> It's very dangerous because:
>> >>> z.d += 1
>> >>> z.d
>> 51
>> (now a object var is created called 'd')
>
>
> And that I agree is confusing! THat is not standard class variable
> behaviour and I personally don't like it. But there isn't any single
> language I know where I like everything about it, so I live with it!
> It's Guido's language, so he gets to choose how features work! :-)
>
>> Is it possible to have 'd' only for the class and not for instances 
>> of this class ?
>
>
> I donl;t think so but it is possible that some of the new metaclass
> stuff might allow that. Also you could probabnly use getattr()/settatr()
> to do something similar.
>
> HTH,
>
> Alan G.
>
>