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Date: Wed, 05 Sep 2012 13:19:24 -0400
From: Dave Angel <d@davea.name>
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To: Hans Mulder <hansmu@xs4all.nl>
Subject: Re: is implemented with id ?
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On 09/05/2012 12:47 PM, Hans Mulder wrote:
> On 5/09/12 17:09:30, Dave Angel wrote:
>> But by claiming that id() really means address, and that those addresses
>> might move during the lifetime of an object, then the fact that the id()
>> functions are not called simultaneously implies that one object might
>> move to where the other one used to be before the "move."
> Whoa!  Not so fast!  The id() of an object is guaranteed to not
> change during the object's lifetime.  So if an implementation
> moves objects around (e.g. Jython), then it cannot use memory
> addresses for the id() function.
Which is equivalent to my point.  I had mistakenly thought that Steven
was claiming it was always an address, and disproving that claim by what
amounts to reductio ad absurdem.

>> I think it much more likely that jython uses integer values for
>> the id() function, and not physical addresses.
> The id() function is guaranteed to return some flavour of integer.
>
> In Jython, the return values are 1, 2, 3, 4, etc., except, of course,
> if you invoke id() on an object you've id'd before, you get the same
> number as before.
>
> In current versions of CPython, you do get the (virtual) memory
> address, converted to an int (or a long).  But then, CPython does
> not move objects.
>
> Maybe the next version of CPython should shift id values two or three
> bits to the right, just to make sure people don't misinterpret ids as
> memory addresses.
>
>

I think i'd prefer if it would put it through one step of a CRC32.

-- 

DaveA