Is 'everything' a refrence or isn't it?

[Bryan Olson]

Fredrik Lundh wrote:
> Bryan Olson wrote:
> 
> 
>>>The identity is not, in itself, a part of the value.
>>>
>>>Python doesn't query the object to determine it's type or identity, but it
>>>always has to query the object to access the value.
>>
>> >
>>
>>>A look at the C implementation of a typical object might help:
>>>
>>>    typedef struct {
>>>        int ob_refcnt;
>>>        struct _typeobject *ob_type; /* type */
>>>        ... an unknown amount of stuff used to represent the value ...
>>>    } MyObject;
>>>
>>>In CPython, the MyObject* pointer is the identity.  The ob_refcnt field is a
>>>CPython implementation detail.  The ob_type field contains the type.
>>
>>So, was it an editing error when you said that Python does not
>>query the object to determine its type?  The type is there in the
>>object, and and in Python, variables and references are not typed.
> 
> 
> do you want to understand this, or do you just want to argue ?

Both!

I think the following is correct: an object's identity is not part
of its value, while its type is.

> (hint: what might the word "query" mean in this context?  can you think
> of a meaning that's compatible with what I wrote?

I don't think usage of "query" is the issue. Python queries
objects for their types; it's now a user-visible feature:

     >>> 'hello'.__class__
     <type 'str'>


 >  would concepts like
> "object", "value", "type", and "identity" be radically different on a python
> implementation that used e.g. "true" garbage collection and tagged pointers
> instead of CPython's approach?  if so, why?)

Python would still be duck-typed and the type would still be a
property of the object. Implementation-wise and behavior-wise,
Python queries objects for their types.


-- 
--Bryan