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

[Terry Reedy]

rurpy at yahoo.com wrote:

> Or one could adopt what Terry Reedy called a
> 4-aspect view: an object is identity, class,
> value (or local-state or something) and
> intrinsic-value.

What I specifically said is id, class, instance attributes, and private 
data.  So objects have only one, some only the other, some both, and 
some neither.  I also noted that the boundary between properties and 
instance methods of the class and attributes of the instance is somewhat 
flexible.

I think the important point is this.  In Python, objects are 
self-identifying bundles of information, which is to say, the bundle 
includes knowledge of the which universe of possible bundles the object 
comes from, where the universe includes a set of operations.  This is 
sometimes called RTTI -- run-time type information.  This is in contrast 
to other languages and signal-processors where information 
(bit-patterns) is usually *not* self-identifying, but the universe must 
be somehow enforced by a compiler or carried in the context.  In C, for 
instance, most types cannot have RTTI and RTTI is only required for 
unions.  Programmers can give structs a type field and that is how 
CPython implements PyObjects.

Terry Jan Reedy