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Date: Thu, 05 Jan 2012 12:13:39 +0100
From: Jean-Michel Pichavant <jeanmichel@sequans.com>
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To: Jean-Michel Pichavant <jeanmichel@sequans.com>
Subject: Re: can a subclass method determine if called by superclass?
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Cc: python-list@python.org, Peter <peter.milliken@gmail.com>
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Jean-Michel Pichavant wrote:
> Peter wrote:
>> Situation: I am subclassing a class which has methods that call other
>> class methods (and without reading the code of the superclass I am
>> discovering these by trial and error as I build the subclass - this is
>> probably why I may have approached the problem from the wrong
>> viewpoint :-)).
>>
>> Problem: when overriding one of these "indirectly called" superclass
>> methods I would like to take differing actions (in the subclass
>> instance) depending on whether it is the superclass or the subclass
>> instance performing the call.
>>
>> Question: Is there any way to determine in a method whether it is
>> being called by the superclass or by a method of the subclass
>> instance?
>>
>> Now I suspect that what I am doing is actually very muddy thinking :-)
>> and I don't want to attempt to explain why I am approaching the design
>> this way as an explanation would require too much work - I will
>> consider an alternative inheritance approach while waiting an answer,
>> but the answer to the question interested me (even if I do a redesign
>> and come up with a more "elegant" approach to the problem).
>>
>> Thanks
>> Peter
>>   
> As you suspected, this is probably the wrong approach.
>
> However since you asked for a solution anyway :o)
>
> class Parent(object):
>  def foo(self):
>    # implementation by subclasses is still REQUIRED
>    if self.__class__ is Parent:
>       raise NotImplementedError()
>    # common code for all foo methods
>    print "calling foo"
>
> class Child(Parent):
>  def foo(self):
>    # You can still call the virtual method which contains some code    
> Parent.foo(self)
>    # here the custom code
>
>
> p = Parent()
> c = Child()
>
>
> c.foo()
> p.foo()
>
> Note that this is not the best approach, still acceptable because 
> there is no code specific to a subclass in the base class.
>
> JM
I just realized I didn't addressed the problem you described, sorry, 
just ignore my mail.

JM