[Cython] python callback

[simon at arrowtheory.com]

> Could anyone give me a tip on how to convert a python function
> of the form
>
> def func(x):
>     return some_operation(x)
>
> to a C function of the form
>
> cdef void cfunc(double x, double *y):
>     y = some_operation(x)

y[0] = some_operation(x)

>
> That is I want to be able to turn a python function into
> a C function with pass by reference return semantics.
>
> I looked at the cheesefinder example, and I am not sure how to adapt it,
> as I
> want to be able to have the user supply the python function, and I can't
> think
> of how to make a cdef callback function that knows what this function is,
> that
> is
>
> cdef void callback(souble x, double *y):
>     y = func(x)
>
> I am not sure how to set func in this way, without rewriting the cdef each
> time. In python I would just use a higher order function . . .

in general, you need an extra "void *" argument in the callback
function (which you would use to pass a python callable).
Well designed C libraries use this convention, but it
sounds like you don't have this.

>
> Thanks,
> Gabriel
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>

Simon.