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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: selective (inheriting?) dir()?
Date: Mon, 21 Apr 2014 17:16:47 -0400
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On 4/21/2014 10:06 AM, Skip Montanaro wrote:
> Before I get up to my neck in gators over this, I was hoping perhaps
> someone already had a solution. Suppose I have two classes, A and B,
> the latter inheriting from the former:
>
> class A:
>      def __init__(self):
>          self.x = 0
>
> class B(A):
>      def __init__(self):
>          A.__init__(self)
>          self.y = 1
>
> inst_b = B()
>
> Now, dir(inst_b) will list both 'x' and 'y' as attributes (along with
> the various under under attributes). Without examining the source, is
> it possible to define some kind of "selective" dir, with a API like
>
>      def selective_dir(inst, class_): pass
>
> which will list only those attributes of inst which were first defined
> in (some method defined by) class_? The output of calls with different
> class_ args would yield different lists:
>
>      selective_dir(inst_b, B) -> ['y']
>
>      selective_dir(inst_b, A) -> ['x']
>
> I'm thinking some sort of gymnastics with inspect might do the trick,
> but after a quick skim of that module's functions nothing leapt out at
> me. OTOH, working through the code objects for the methods looks
> potentially promising:
>
>>>> B.__init__.im_func.func_code.co_names
> ('A', '__init__', 'y')
>>>> A.__init__.im_func.func_code.co_names
> ('x',)

You can permanently affect dir(ob) with a special method.

object.__dir__(self)

     Called when dir() is called on the object. A sequence must be 
returned. dir() converts the returned sequence to a list and sorts it.

 From outside the class, you get the attributes defined directly in a 
class klass as the difference of set(dir(klass) and the union of 
set(dir(base)) for base in klass.__bases__. To include attributes set in 
__new__ and __init__, replace klass with klass().

-- 
Terry Jan Reedy