Official definition of call-by-value (Re: Finding the instance reference...)

[Arnaud Delobelle]

Derek Martin <code at pizzashack.org> writes:

> On Thu, Nov 13, 2008 at 11:58:18AM -0800, rurpy at yahoo.com wrote:
>> I have yet to see any reasonable definition of a Python value in the
>> Python docs or elsewhere, despite the fact that a value is one of
>> the three defining characteristics of an object, a central concept
>> in Python.
>
> Why does it need to be defined in the Python docs?  Is this really
> even an important question to answer?  Are you unable to write correct
> functional programs in Python without having it answered?  I suspect
> it's not an issue...
>
> Let's assume for the moment that it is, though.  The term "value"
> already has a meaning... the one ascribed to it by its use in natural
> language.  One on-line dictionary includes this among its definitions:
>
>   magnitude; quantity; number represented by a figure, symbol, or the
>   like: the value of an angle; the value of x; the value of a sum.
>
> It seems clear that this, or something extremely close to this, is
> what is meant in the Python docs by the unqualified use of the term.

I reiterate that IMO the 'value' of an object is not really a useful
concept.

E.g. think of the integer 3.  It has a representation ('3'), it compares
to other objects (via int.__eq__, int.__lt__, etc), you can perform
arithmetic operations on it (via int.__add__, int.__sub__, etc), etc.
What more would you want to know about it?

[...]
> If you like, you could think of the value of an object as the set of
> all possible values to which the object may evaluate in every possible
> context, given a particular state of the object.

This definition looks a bit circular to me ;)

-- 
Arnaud