> I choosed to use consistent result type. But now I would prefer int :-) I see 
> that PyInt_FromSize_t() returns a long if the value doesn't fit in an int. So 
> it's correct.

Cool.  I think int is better, simply because the result is almost always going to fit 
into an int in practice, and because calculations with ints are faster.

> I'm paranoid

Yeah, me too.  I removed the check, but also changed the assert to check that
Py_SIZE is nonzero.

> Can you fix these two issues (use PyInt_FromSize_t and remove the if)?

Done.