[Cython] Problem with cdef long

[Robert Bradshaw]

On Jun 2, 2008, at 12:51 PM, Simon King wrote:

> Dear Cython team,
>
> hopefully the following really is a cython-question, not a Sage- 
> question.
>
> Write a file Problem.pyx:
>
> ctypedef struct Term_t:
>     long coef
>
> cdef class Term:
>     cdef Term_t Data
>     def __init__(self, c):
>         self.Data.coef = c
>     def coefficient(self):
>         return self.Data.coef
>
>
> Start Sage and do
>  sage: attach Problem.pyx
>  sage: T=Term(3)
>  sage: type(T.coefficient())
>
> Then the result is
>  <type 'int'>
> and *not* <type 'long'>!
>
> Why is it of type 'int' although coef is defined 'long' in Term_t?

I think your confusion here is over the difference between C ints/ 
longs/etc. and Python ints/longs. The Python "int" type is a Python  
object that wraps a C long. Python "long" type is an arbitrary- 
precision integer. Your Term.coefficient function returns a Python  
object, so it takes the self.Data.coef (which is a C long) and wraps  
it in a Python object (of type "int").

> How can i avoid this automatic down-grading of coef?
>
> I really want coef to be of type 'long', since 'int' isn't good  
> enough in
> my application.

When you say "int" isn't good enough, do you mean you need arbitrary  
precision? Because there isn't a (simple) C type that will give you  
that (you would have to use mpz_t or something like that).

- Robert