Static variable vs Class variable

[Hrvoje Niksic]

paul.melis at gmail.com writes:

> Right, the paragraph is actually pretty clear after a second
> reading.  I find it surprising nonetheless, as it's easy to forget
> to return a result when you're implementing a method that does an
> in-place operation, like __iadd__:

I've recently been bitten by that, and I don't understand the
reasoning behind __iadd__'s design.  I mean, what is the point of an
*in-place* add operation (and others) if it doesn't always work
in-place?