On Fri, Jul 08, 2011 at 09:47 +0200, Maciej Fijalkowski wrote:
> On Fri, Jul 8, 2011 at 1:49 AM, Alex Gaynor <alex.gay...@gmail.com> wrote:
> > Hi all,
> > I've now spoken with several developers about the object identity that
> > arises out of hte new dict strategies, and all seem to think that the
> > current implementation breaks Python's semantics, that is:
> > x = 3
> > z = {x: None}
> > assert next(iter(z)) is x
> > will fail. The only solution I see to this that maintains the correct
> > semantics in all cases is to specialize is/id() for primitive types. That
> > is to say, all integers of any given value have the same id() and x is y is
> > true. Doing x is y is true is easy, you simply have a multimethod which
> > dispatches on the types and compares intval for W_IntObjects (objects of
> > differing types can never have the same identity) however the question is
> > what to use for id() that is unique, never changes for an int, and doesn't
> > intersect with any other live object. In particular the last constraint is
> > the most difficult I think.
> > Alex
>
> >>> x = 3
> >>> x is 3
> True
> >>> x = 1003
> >>> x is 1003
> False
> >>>
I guess this is not what Alex means here.
In CPython, PyPy (both 1.5 and trunk) you can do:
>>> class A: pass
>>> a=A()
>>> next(iter({a: None})) is a
True
but not with ints on pypy-trunk
>>> a=3
>>> next(iter({a: None})) is a
False
(it's true on pypy-1.5).
IOW, i think the issue here is that iterating over keys of a dict usually
gives the exact same ("is") objects in CPython whereas pypy trunk does not
provide that at least for ints.
best,
holger
> Stop relying on obscure details I think
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