Explanation of list reference
marko at pacujo.net
Sat Feb 15 17:29:59 CET 2014
Steven D'Aprano <steve+comp.lang.python at pearwood.info>:
> On Sat, 15 Feb 2014 14:07:35 +0200, Marko Rauhamaa wrote:
>> Steven D'Aprano <steve+comp.lang.python at pearwood.info>:
>>> On Sat, 15 Feb 2014 12:13:54 +0200, Marko Rauhamaa wrote:
>>>> 5. id(x) == id(y) iff x is y
>>> # Counter-example
>>> py> x = 230000
>>> py> idx = id(x)
>>> py> del x
>>> py> y = 420000
>>> py> idy = id(y)
>>> py> idx == idy
>> I don't accept that as a counterexample.
Nowhere do I see the violating "x is y".
> All I need to do is show a case where two distinct objects have the
> same ID.
How do you know objects are "distinct"? Myself, I would use the "is"
>> That's the point. I don't think id() and "is" have any abstract
>> meaning on top of the formal axioms.
> Who is talking about "abstract meaning"?
I am. I mean, "implementation-independent".
> Object identity is simple and well-defined in Python. I don't know why
> you are so resistant to this. Read the documentation.
It is not defined at all:
Every object has an identity, a type and a value. An object’s
identity never changes once it has been created; you may think of it
as the object’s address in memory. The ‘is‘ operator compares the
identity of two objects; the id() function returns an integer
representing its identity.
Thus "x and y are identical" *means* "x is y" and nothing else.
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