can a subclass method determine if called by superclass?

Thu Jan 5 06:09:41 EST 2012

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