How to pass a pointer to an external program in Cython

Question

I am trying to write a wrapper around a C program so that I can call it from Python. I am using Cython for this. The C function takes a callback function as an argument, but this callback function will only be known at runtime of the python program. I was looking for how to do this and it seems like there is no easy solution, but the following seems to work:

#python.py

libc = cdll.LoadLibrary("myfunc.so") #Callback function is defined in myfunc.so 
....
c_wrapper(libc.fun, ...)

.

#c_wrapper.pyx

cdef extern void mainfunction(void *F, ...) #The intial C function we are wrapping
ctypedef void (*myfuncptr) () 

def c_wrapper(f, ...) # our function pointer is passed to the wrapper as a Python object
    cdef myfuncptr thisfunc
    thisfunc = (<myfuncptr*><size_t>addressof(f))[0]
    mainfunction(thisfunc, ...)

This method works for C and FORTRAN functions (assuming it will work for most compiled languges) and Python functions (using C types), but this seems a bit inconvenient. Is there an even easier way to do this in Cython?

thank

EDIT: I can't change the C library I'm trying to wrap

Answer 1

, ?

Python C?

: , . Demos/callback/ Cythona >

, , , . , :

/* lib.c -> lib.so */
#include <stdio.h>

void fn1(void) {
        puts("Called function 1");
}

void fn2(void) {
        puts("Called function 2");
}

,

/* main.c -> main.so */

typedef void (*callback)();

void mainfunction(void *F) {
        ((callback)F)();
}

Python:

>>> from ctypes import cdll
>>> lib = cdll.LoadLibrary('./lib.so')
>>> main = cdll.LoadLibrary('./main.so')
>>> main.mainfunction(lib.fn1)
Called function 1
>>> main.mainfunction(lib.fn2)
Called function 2

, Python:

>>> from ctypes import CFUNCTYPE
>>> def pyfn():
...     print "Called the Python function"
... 
>>> CWRAPPER = CFUNCTYPE(None)

>>> wrapped_py_func = CWRAPPER(pyfn)
>>> main.mainfunction(wrapped_py_func)
Called the Python function