using __getitem()__ correctly

[Charles T. Smith]

On Thu, 31 Dec 2015 11:21:59 +1100, Ben Finney wrote:

> Steven D'Aprano <steve at pearwood.info> writes:
> 
>> On Thu, 31 Dec 2015 10:13 am, Ben Finney wrote:
>>
>> > You may be familiar with other languages where the distinction
>> > between “attribute of an object” is not distinct from “item in a
>> > dictionary”. Python is not one of those languages; the distinction is
>> > real and important.
...
> 
> Tersely: the relationship between an object and its attributes, is not
> the same as the relationship between a dictionary and its items.


I understand this to mean that the relationship between a dictionary and
its items is less complex than the relationship between an object and
its attributes.


I'd like to catalog the different attribute types/implications:
- perhaps a hierarchy of meta-ism - or user-relevance
- those things in the __dict__
- those things not in the __dict__ but without the "__"
- ???


> 
>> Obviously there is a syntax difference between x.attr and x['key']
> 
> Not merely syntax; the attributes of an object are not generally
> available as items of the container.


What are the set of ways that an attribute is accessible?  Including
implementation implications?

 
> 
>> Either the instance __dict__, the class __dict__, or a superclass
>> __dict__.
> 
> No, I'm not referring to the ‘__dict__’ attribute of an object; I'm
> referring to the object itself.
> 
> To talk about the attributes of an object ‘foo’ is distinct from talking
> about the items in a dictionary ‘foo’. That distinction is real, and
> important.


But wanting to deal with the attributes of an object without considering
the way it's implemented - although possible - requires a complete virtual
model that covers all implications.  It's easier to simply understand how the
objects work under the covers.