Question about the definition of the value of an object

[Iwo Herka]

> Attempting to define value here would be at best a massive
> distraction from the concepts the documentation is trying
> to get across.

> There is one very simple definition of "value" which is entirely
> accurate, but probably not helpful, and that is: An object's
> value is whatever it is equal to.

> Generally, Python objects have their values defined by an abstract
> concept that is being represented.

That confirms my intuition. Thank you for the responses.

Sincerely,
Iwo Herka
pon., 19 lis 2018 o 20:46 Chris Angelico <rosuav at gmail.com> napisał(a):
>
> On Tue, Nov 20, 2018 at 3:08 AM Iwo Herka <iwoherka at gmail.com> wrote:
> >
> > Hello everyone,
> >
> > I've been looking for something in the documentation
> > (https://docs.python.org/3.8/reference/datamodel.html) recently
> > and I've noticed something weird. Documentation states that every
> > object has a value, but doesn’t provide any definition
> > whatsoever of what the value is. Now, I'm sure that every reasonably
> > fluent Python programmer has an intuitive
> > understanding of the term, nonetheless, I would expect the
> > documentation defines it somehow (not necessarily
> > in a formal fashion), especially considering that "the value of an
> > object" is used to explain other concepts, such as
> > mutability:
> >
> > > The value of some objects can change. Objects whose value can change are said to be mutable; objects whose
> > value is unchangeable once they are created are called immutable.
> >
> > So, why is documentation silent on this? One reason I can think of is
> > to avoid answering inconvenient questions.
>
> Sorta kinda, yeah. There is one very simple definition of "value"
> which is entirely accurate, but probably not helpful, and that is: An
> object's value is whatever it is equal to. That is to say, you can ask
> two basic questions about an object:
>
> x is y # identity: are x and y the SAME object?
> x == y # equality: do x and y have the same value?
>
> Value and equality are intrinsically linked, but unfortunately that
> doesn't really explain what either one actually IS. As Rhodri says,
> you can ask a philosopher about that, and will be stuck for weeks :)
>
> The concept of "immutable" vs "mutable" object, therefore, is that
> some objects may compare equal now and unequal later. Since the same
> object is able to change in "value" over time, it may become (un)equal
> to something while still being the same object. Thus mutable objects
> can't be used as dict keys, as their values could change, and dict
> lookups have to match based on equality. (Imagine putting two keys
> into a dict while they have different values, and then mutating one of
> them to have the same value. Now try to look up that new value using a
> third object. The Logic Police will arrest you before you can say
> "hashability"!)
>
> Generally, Python objects have their values defined by an abstract
> concept that is being represented. For instance, the integer 32 and
> the float 32.0 have the same value, even though they're different
> types; they both represent the abstract number equal to
> two-to-the-fifth. But right here in that sentence, you can see how
> hard it is to actually *define* that value. At best, all you can
> really say is that the value is equal to the value of int("32") or
> some other way of getting an object with that value.
>
> Yep, it's hard. But the cool thing is, it usually doesn't matter - you
> can say "x has the value 32" without worrying about representations,
> data types, etc.
>
> ChrisA
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