Terminology: "reference" versus "pointer"

[Akira Li]

Steven D'Aprano <steve at pearwood.info> writes:

> On Mon, 14 Sep 2015 01:23 pm, Akira Li wrote:
>
>> Steven D'Aprano <steve at pearwood.info> writes:
>> 
>>> On Mon, 14 Sep 2015 11:22 am, Akira Li wrote:
>>>> Look at the last example:
>>>> http://thread.gmane.org/gmane.comp.python.general/782626/focus=782704
>>>
>>>
>>> I'm afraid that page is broken in my browser. Can you not summarise, or
>>> link to the specific message? I may be able to use another browser in a
>>> day or two, but hopefully the discussion will have moved on by then.
>> 
>> https://mail.python.org/pipermail/python-list/2015-September/696631.html
>
> Thanks. You mean this example?
>
>   lst = [range(1, 3) for _ in range(3)]
>   a = [lst[0], lst[0]]
>   b = [lst[1], lst[2]]
>
>
> I don't see what's difficult about this example. Here's a simple ASCII
> drawing:
>
>
> lst --------> [ range-object-1 , range-object-2 , range-object-3 ]
>
> a ----------> [ range-object-1 , range-object-1 ]
>
> b ----------> [ range-object-2 , range-object-3 ]
>

I should have mentioned that lst plays the role of range-object-X in
your diagram i.e., only *a*, *b* names actualy exits (I should add `del
lst` to the example) -- as the original example requires.


> Trying to draw an arrow diagram using text is not my idea of a good time,
> but I'll give it a go. Requires a monospaced font and an email client that
> won't reflow the text:
>
>       +-----+------+
>       |     |      | <--------------------------- a
>       +--|--+---|--+
>          |      |
>          |      |
>          V      |
>       +-----+ <-+             +----+
>       |range| <---------------|-   |<------------ lst 
>       +-----+                 +----+
>                   +-----------|-   |
>       +-----+     |           +----+
>   +-> |range| <---+    +------|-   |
>   |   +-----+          |      +----+
>   |                    |
>   |   +-----+          |
>   |   |range| <--------+
>   |   +-----+
>   |      ^
> +-|-+    |
> |   |    |
> +---+    |
> |  -|----+
> +---+
>   ^
>   |
>   +------------------------------------------- b
>
>
> Out of the two, I know which one I prefer.

I don't know what it means. If you mean "box and arrows" is superior
somehow then I don't see any difference from the "parcel tags" model
here.

My point is that neither models are detailed enough to describe
meaningfully the behavior of Python code in the general case.