[Pyrex] Re: Wrapping _randommodule.c

[Robert Kern]

Simon Frost wrote:
> Dear Pyrex List,
> 
> I'd like to be able to access the internals of the RandomType object, as
> defined in _randommodule.c, so I can generate random numbers within C
> code. It's defined as follows:
> 
> typedef struct {
>     PyObject_HEAD
>     unsigned long state[N];
>     int index;
> } RandomObject;
> 
> Random numbers are then generated using:
> 
> static PyObject * random_random(RandomObject *self);
> 
> What I would like to do is to generate a random number class generated
> within Python
> 
>>> import random
>>> rng=random.Random(1)
> 
> and then pass it to functions in Pyrex.
> 
> My questions are:
> 1. How do I link against _randommodule?

You don't. It doesn't expose a C API; you can't call random_random()
from other extension modules.

> 2. RandomObject is a struct containing a PyObject, which Pyrex doesn't
> like. What's the usual workaround (except pass)?

No, it *is* a PyObject. You don't put PyObject_HEAD in the Pyrex struct
definition. You would do something like the following, I believe:

ctypedef class _random.Random [object RandomObject]:
    cdef unsigned long state[624]
    cdef int index

I recently added Mersenne Twister PRNG support for scipy_core. Since I
couldn't use _random's implementation, I used a small implementation
called RandomKit. You can see the code here:

http://svn.scipy.org/svn/scipy_core/branches/newcore/scipy/corelib/mtrand/

You can sync it with a random.Random() instance, if you must, by
getting/setting the state.

-- 
Robert Kern
rkern at ucsd.edu

"In the fields of hell where the grass grows high
 Are the graves of dreams allowed to die."
  -- Richard Harter