Raj Bandyopadhyay wrote:
> Hi
>
> Here's a simple class example I've defined
>
> #############################
> class myInt(int):
> def __add__(self,other):
> return 0
>
> print 5 + myInt(4) #prints 9
> print myInt(4) + 5 #prints 0
> #############################
>
> The Python binary operation function (binary_op1() in
> Objects/abstract.c) states
> the rules for binary operations as follows:
>
> v w Action
> -------------------------------------------------------------------
> new new w.op(v,w)[*], v.op(v,w), w.op(v,w)
> new old v.op(v,w), coerce(v,w), v.op(v,w)
> old new w.op(v,w), coerce(v,w), v.op(v,w)
> old old coerce(v,w), v.op(v,w)
>
> [*] only when v->ob_type != w->ob_type && w->ob_type is a subclass of
> v->ob_type
>
>
> It seems that my example should fall in case 1, and in both cases, the
> __add__ function of the subclass should be used, returning 0, regardless
> of operand order. However, in one case the subclass's function is used
> and not in the other case. What am I missing here?
>
> Thanks
> Raj
>
i think that you need to use __radd__ for addition with custom object on right
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