[Python-Dev] PEP 203 Augmented Assignment

[Guido van Rossum]

[Guido]
> > Second, what should happen to a slice assignment?

[Ping]
> My vote is: nothing!  (Read on.)
> 
> > The basic slice form is:
> > 
> >   a[i:j] += b
> 
> What does this mean?  I don't see how it could be any different from:
> 
>     a[j:j] = b

Apparently you haven't used NumPy arrays (matrices).  I haven't
either, but I hear they overload + so that A+B is elementwise
addition, and you can write A+1 to add 1 to each element of A.
Thus, for a NumPy programmer, A += 1 would certainly look like A =
A+1, and similar for A += B.

> It looks to me like going through various contortions to support
> augmented assignment to slices is not going to be worth the trouble.
> 
> May i suggest
> 
>     >>> a[i:j] += b
>     SyntaxError: augmented assignment to a slice is not allowed

That's what I thought too until I realized that for NumPy arrays
slice+= makes sense.

--Guido van Rossum (home page: http://www.pythonlabs.com/~guido/)