On Mar 7, 2009, at 12:10 AM, Simon King wrote:

> Hi!
>
> I would like to create an extension class that inherits from
> CommutativeRingElement. In order to learn how it works, I looked at
> the file sage/rings/polynomial/multi_polynomial.pyx and ...pxd
>
> However, the whole story fails at a *very* basic level: Just for
> testing, I copied both files multi_polynomial.pyx and
> multi_polynomial.pxd into some directory, and in this directory I said
>  sage: attach multi_polynomial.pyx
>
> It failed in the line
>    cdef class MPolynomial(CommutativeRingElement):
> with the message
>    'CommutativeRingElement' is not declared
>
> Why?
>
> Is 'attach' the wrong thing to do if there is a .pxd file around?

Note that you only need a .pxd file for other stuff to inherit from  
you. Also, attach works with ".spyx" files (basically .pyx files, I'm  
not sure why we have that distinction).

- Robert



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