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Re: instance.attribute lookup

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  Re: instance.attribute lookup Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-05 17:29 -0600

#30851 — Re: instance.attribute lookup

On Fri, Oct 5, 2012 at 11:39 AM, Ethan Furman <ethan@stoneleaf.us> wrote:
> There is a StackOverflow question [1] that points to this on-line book [2]
> which has a five-step sequence for looking up attributes:
>
>> When retrieving an attribute from an object (print
>> objectname.attrname) Python follows these steps:
>>
>> 1. If attrname is a special (i.e. Python-provided) attribute for
>> objectname, return it.
>>
>> 2. Check objectname.__class__.__dict__ for attrname. If it exists and
>> is a data-descriptor, return the descriptor result. Search all bases
>> of objectname.__class__ for the same case.
>>
>> 3. Check objectname.__dict__ for attrname, and return if found. If
>> objectname is a class, search its bases too. If it is a class and a
>> descriptor exists in it or its bases, return the descriptor result.
>>
>> 4. Check objectname.__class__.__dict__ for attrname. If it exists and
>> is a non-data descriptor, return the descriptor result. If it exists,
>> and is not a descriptor, just return it. If it exists and is a data
>> descriptor, we shouldn't be here because we would have returned at
>> point 2. Search all bases of objectname.__class__ for same case.
>>
>> 5. Raise AttributeError
>
> I'm thinking step 1 is flat-out wrong and doesn't exist.  Does anybody know
> otherwise?

I think step 1 refers to looking up attributes like "foo.__class__" or
"foo.__dict__" themselves.

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