ctypes invalid result type for a callback function

I face a problem while implementing with ctypes. I have 2 C functions:

antichain** decompose_antichain(antichain*, int, char (*)(void*, void*), void** (*)(void*));
counting_function** decompose_counting_function(counting_function*);

where antichain and counting_function are two structures. An antichain can be seen like a set, containing elements of unknown type (in this exemple, counting_function). The decompose_antichain function takes as argument (amongst other things) the function to use to decompose the elements the antichain contains (-> a function of which the prototype is void** (*) (void*)).

Now i would like to use decompose_antichain from Python. I used ctypes:

lib = cdll.LoadLibrary("./mylib.dylib")
#CountingFunction, Antichain and other definitions skipped
DECOMPOSE_COUNTING_FUNCTION_FUNC = CFUNCTYPE(POINTER(c_void_p), POINTER(CountingFunction))
开发者_Go百科decompose_counting_function_c = lib.decompose_counting_function
decompose_counting_function_c.argtypes = [POINTER(CountingFunction)]
decompose_counting_function_c.restype = POINTER(c_void_p)
decompose_antichain_c = lib.decompose_antichain
decompose_antichain_c.argtypes = [POINTER(Antichain), c_int, DECOMPOSE_COUNTING_FUNCTION_FUNC, COMPARE_COUNTING_FUNCTIONS_FUNC]
decompose_antichain_c.restype = POINTER(POINTER(Antichain))

(...)

antichains_list = decompose_antichain_c(antichain, nb_components, COMPARE_COUNTING_FUNCTIONS_FUNC(compare_counting_functions_c), DECOMPOSE_COUNTING_FUNCTION_FUNC(decompose_counting_function_c))

The last line produces the error: invalid result type for a callback function.

I can't see where the problem come from. Can anyone help me? Thanks

You need to make sure the argtypes and result types match. It looks like you swapped the argument types of decompose_antichain_c. You have DECOMPOSE_COUNTING_FUNCTION_FUNC, COMPARE_COUNTING_FUNCTIONS_FUNC in the argtypes, which doesn't match the declaration of the C function you gave above. You then try to call it with COMPARE_COUNTING_FUNCTIONS_FUNC first, and DECOMPOSE_COUNTING_FUNCTION_FUNC second.

DECOMPOSE_COUNTING_FUNCTION_FUNC also looks wrong. It should probably be CFUNCTYPE(POINTER(c_void_p), c_void_p) just guessing from the rest of the code.

I can give a more detailed answer if you provide the code that creates COMPARE_COUNTING_FUNCTIONS_FUNC and CountingFunction