If there are only two versions of the structure on all operating systems, we 
can add a check in configure (e.g. test the size of the ident attribute, =int 
or >=void*?) to define a macro (e.g. HAVE_OPENBSD_KEVENT_STRUCT). You might be 
able to change the type of the fields in the Python structure at run time (in 
select module init), but I prefer to do it at compile time! Or you can add 
*checks* at runtime (at select init) on the size of the fields.