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is implemented with id ?

Hans Mulder hansmu at xs4all.nl
Wed Sep 5 09:48:18 EDT 2012 
On 5/09/12 15:19:47, Franck Ditter wrote:
> Thanks to all, but :
> - I should have said that I work with Python 3. Does that matter ?
> - May I reformulate the queston : "a is b" and "id(a) == id(b)"
>   both mean : "a et b share the same physical address". Is that True ?

Yes.

Keep in mind, though, that in some implementation (e.g.
Jython), the physical address may change during the life
time of an object.

It's usually phrased as "a and b are the same object".
If the object is mutable, then changing a will also change b.
If a and b aren't mutable, then it doesn't really matter
whether they share a physical address.

Keep in mind that physical addresses can be reused when an
object is destroyed.  For example, in my Python3,


id(math.sqrt(17)) == id(math.cos(17))

returns True, even though the floats involved are different,
because the flaots have non-overlapping lifetimes and the
physical address happens to be reused.


Hope this helps,

-- HansM
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