[Tutor] The trap of the year

[Izz ad-Din Ruhulessin]

I think it has something to do with the physical id of the object

2011/1/25 Karim <karim.liateni at free.fr>

>
> Hello All,
>
> Just to share on rageous bug I encounter where 2 lists which "should" to be
> different (same id) because hold by different instances of the same class
> are not in fact DIFFERENT, see below:
>
> >>> class Device():
> ...     def __init__(self, parameters=[]):
> ...         self.parameters = parameters
> ...     def param(self):
> ...         print(id(self.parameters))
> ...
> >>> a=Device()
> >>> b=Device()
> >>> a.param()
> 140559202956568
> >>> b.param()
> 140559202956568
>
> When I discovered that I was puzzled because at the prompt:
>
> >>> a = []
> >>> b = []
> >>> id(a)
> 140559202956496
> >>> id(b)
> 140559202957000
>
> I am not really understanding why my init in the class made it refers to
> the same list object.
> What is the difference with 2nd example directly at the prompt?
>
> By the way, this one is ok:
>
> >>> class Device():
> ...     def __init__(self,parameters=None):
> ...         self.parameters = None
> ...         self.parameters = []
> ...     def param(self):
> ...         print(id(self.parameters))
> ...
> >>> a=Device()
> >>> b=Device()
> >>> b.param()
> 140559202956496
> >>> a.param()
> 140559202956568
>
> Karim
>
>
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