Newbie inheritance problem

[Michael Hudson]

zzzzz <zzizz_ at notmail.com> writes:

> Hi all, I have overwridden the __add__ method for a class, then built
> a class based on the above class; however, the object I'm returning is
> of the base class not the inherited class. If that doesn't make sense
> see below:
> 
> class A:
>     def __init__(self,value=0.0)
>         self._value=float(value)
>     def __add__(self,other)
>         return A(self._value+other._value)
> 
> class B(A):
>     pass
> 
> x=B(3)
> y=B(2)
> z=x+y
> 
> The way I've done it z becomes an instance of A not B!!! How do I do
> it correctly? Do I have to override all the __add__, __sub__, etc...
> methods?

Well, you can do this:

class A:
    def  __init__(self,value=0.0)
        self._value=float(value)
    def __add__(self,other)
        return self.__class__(self._value+other._value)

HTH,
M.

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