__iadd__ useless in sub-classed int

[Diez B. Roggisch]

samwyse schrieb:
> For whatever reason, I need an inproved integer.  Sounds easy, let's
> just subclass int:
> 
>>>> class test(int):
> 	pass
> 
> Now let's test it:
> 
>>>> zed=test(0)
>>>> zed.__class__
> <class '__main__.test'>
>>>> zed
> 0
> 
> So far, so good.  Now let's try incrementing:
> 
>>>> zed+=1
>>>> zed
> 1
>>>> zed.__class__
> <type 'int'>
> 
> WTF??!
> Is this a bug or is it the inevitable result of optimizing for the
> case where all integers are indistinguishable?

There has been a lengthe thread over the semantics of __iadd__ a few 
weeks ago. It _can_ modify the object in question in-place (something 
not possible for ints anyway), but it will ALWAYS return a reference 
which will be set to the left-hand-side.

zed = zed.__iadd__(1)

So - you need to overload the __iadd__-method to return a test-instance.

Diez