When is a subclass not right?

[Simon Forman]

Chaz Ginger wrote:
> I was writing some code that used someone else class as a subclass. He
> wrote me to tell me that using his class as a subclass was incorrect. I
> am wondering under what conditions, if ever, does a class using a
> subclass not work.
>
> Here is an example. For instance the original class might look like:
>
> class A :
>   def __init__(self,arg) :
> 	self.foo = arg
>   def bar(self) :
> 	return self.foo
>
>
> And I defined a class B1 which looked like:
>
>
> class B1(A);
>   def __init__(self,a1,a2) :
> 	self.c = a1
> 	A.__init__(self,ag)
>
>
> He said I should use it this way:
>
> class B2:
>   def __init__(self,a1,a2):
> 	self.c = a1
> 	self.t = A(a2)
>
>   def bar(self) :
> 	self.t.bar()
>
>
> Other than the obvious difference of B2 having an attribute 't', I can't
> see any other obvious differences. Is there something I am missing?
>
> TIA
> Chaz

When the developer *tells* you it won't work, that's a good indication.
 :-)

You haven't missed anything:  the developer was talking about his
specific code, not python in general.  (I'm on the Twisted list too.
;-) )

Peace,
~Simon