On 20/11/2018 00:14, Chris Barker via Python-Dev wrote:
On Mon, Nov 19, 2018 at 1:41 AM Antoine Pitrou <solip...@pitrou.net
<mailto:solip...@pitrou.net>> wrote:
I'd rather keep the reference to memory addressing than start
doing car
analogies in the reference documentation.
I agree -- and any of the car analogies will probably be only valid in
some jurisdictions, anyway.
I think being a bit more explicit about what properties an ID has, and
how the id() function works, and we may not need an anlogy at all,
it's not that difficult a concept. And methions that in c_python the
id is (currently) the memory address is a good idea for those that
will wonder about it, and if there is enough explanation, folks that
don't know about memory addresses will not get confused.
...
I suggest something like the following:
"""
Every object has an identity, a type and a value. An object’s identity
uniquely identifies the object. It will remain the same as long as
that object exists. No two different objects will have the same id at
the same time, but the same id may be re-used for future objects once
one has been deleted. The ‘is’ operator compares the identity of two
objects; the id() function returns an integer representing its
identity. ``id(object_a) == id(object_b)`` if and only if they are the
same object.
**CPython implementation detail:** For CPython, id(x) is the memory
address where x is stored.
"""
I agree that readers of a language reference should be able to manage
without the analogies.
I want to suggest that identity and id() are different things.
The notion of identity in Python is what we access in phrases like "two
different objects" and "the same object" in the text above. For me it
defies definition, although one may make statements about it. A new
object, wherever stored, is identically different from all objects
preceding it.
Any Python has to implement the concept of identity in order to refer,
without confusion, to objects in structures and bound by names. In
practice, Python need only identify an object while the object exists in
the interpreter, and the object exists as long as something refers to it
in this way. To this extent, the identifier in the implementation need
not be unique for all time.
The id() function returns an integer approximating this second idea.
There is no mechanism to reach the object itself from the result, since
it does not keep the object in existence, and worse, it may now be the
id of a different object. In defining id(), I think it is confusing to
imply that this number *is* the identity of the object that provided it.
Jeff Allen
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