[Python-Dev] __contains__ hook

[Guido van Rossum]

>  > Because if we add a slot to the as_sequence struct, old extensions
>  > that haven't been recompiled will appear to have garbage in that slot
>  > (because they don't actually have it).  When we use a spare slot in
>  > the main type struct, that problem doesn't exist; but the as_sequence
>  > struct and friends don't have spares.
> 
>   Good point.  I still think a spare slot should be used so sets don't 
> have to look like sequences.

But they won't have to -- all the other pointers in the as_sequence
struct can be NULL.  (This used to be not the case, but I've finally
given in and added NULL tests everywhere -- it was a recurring
complaint from extension writers.)

--Guido van Rossum (home page: http://www.python.org/~guido/)