None, True, False, integers and strings are not mutable. The only time
the id is the "same" between two objects is if they are the identical
two objects.
I'm aware of that. ;-)
CPython just (as a performance optimization) re-uses the same objects
sometimes even if people think they're using different objects.
In,
>>> a = 2
>>> b = 2
Integers are immutable so it was not part of my question.
Christian's point is, I believe, that this is all an implementation
detail to the CPython platform and not a language-defined feature.
Other implementations may do other things, so one should not rely on
this behavior. Basically, don't use "is" unless you really know what
you're doing -- or are testing verses a singleton :) "is" is never the
right thing for numbers. Usually. Ahem.
Well, I now understand that this is also "theoretically" correct:
>>> id({}) == id({})
True
The explanation is that you can only distinguish two objects if ARE
objects, e.g. they both must exist. In the one-liner above, the dict
objects are not directly compared, and they are not BOTH alive when
their ids are taken, so this one liner is a meaningless expression. :-)
I'm always amazed how logical and clean Python is. I do not want to
start flame here, but for other programming languages (like XXX :-) )
they could not even start a thread like this, because some terms and
concepts in other languages are not defined precisely.
L
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