Passing a callback from Python to C by structure

Question

Passing a callback from Python to C by structure

I am trying to pass a callback function from Python to C contained in a struct. So far I've had no luck on how to pass a Python function to C.

Definition of structure C:

typedef int (* TOUCH_CALLBACK_FUNC)(int x, int y);
typedef int (* HARDKEY_CALLBACK_FUNC)(int key);

typedef struct _rect
{
    u32 left;
    u32 top;
    u32 width;
    u32 height;  
} RECT;

typedef struct _touch_data
{
    u8  sign[16];
    u8  *file;
    RECT rect;
    u32 destWidth;
    u32 destHeight;
    u32 uiTimeOut;
    TOUCH_CALLBACK_FUNC cb;
    HARDKEY_CALLBACK_FUNC keyCb;
    void *extArg;
    void *extArg2;
} TOUCH_DATA;

Python definition is as follows

from ctypes import Structure, CFUNCTYPE, c_int32, POINTER

TOUCH_CALLBACK_FUNC = CFUNCTYPE(c_int32, POINTER(c_int32), POINTER(c_int32))
HARDKEY_CALLBACK_FUNC = CFUNCTYPE(c_int32, POINTER(c_int32))

class Rect(Structure):
    _pack_ = 1
    _fields_ = [('left', c_int32),
                  ('top', c_int32),
                  ('width', c_int32),
                  ('height', c_int32)]

class TouchDataStruct(Structure):
    _pack_ = 1
    _fields_ = [('sign', c_char * 16),
                  ('file', c_char_p),
                  ('rect', Rect),
                  ('destWidth', c_uint32),
                  ('destHeight', c_uint32),
                  ('touchCallback', TOUCH_CALLBACK_FUNC),
                  ('keyCallback', HARDKEY_CALLBACK_FUNC),
                  ('uiTimeOut', c_uint32),
                  ('extArg', c_void_p),
                  ('extArg2', c_void_p)]

I am executing the following code from Python:

def touch_cb(x, y):
    return 0


def key_cb(key):
    return 0

data = TouchDataStruct(
    file='...'.encode('ascii'),
    rect=Rect(left=0,top=0,width=50,height=25),
    cb=TOUCH_CALLBACK_FUNC(touch_cb),
    keyCb=TOUCH_CALLBACK_FUNC(key_cb),
    destWidth=75,
    destHeight=30,
    uiTimeOut=60000
)

cwrapper.process(data)

The actual error is that size_t

for the structure that C accepts is 48 and the size_t

actual structure for C is 64.

To get the structure in C, I use the following snippet:

PyObject *Wrapper_Process(PyObject *self, PyObject *args) {
    TOUCH_DATA *touch_data;
    size_t size;

    PyArg_ParseTuple(args, "y#", &touch_data, &size);
    if (size != sizeof(TOUCH_DATA)) {
        // Raise error here!
    }
}