[capi-sig] (no subject)

Philip Semanchuk philip at semanchuk.com
Sat Apr 5 20:12:00 CEST 2014

On Mar 22, 2014, at 12:50 PM, sagar masuti <sagar.masuti at gmail.com> wrote:

> Is it possible to cast an int to a class type ?

Not safely.

> How can I typecast the address passed from C to a class type in python so
> that i can access those class parameters or indirectly saying accessing the
> structure parameters?

I had to do something similar to support the passing of a C pointer (memory address) for my sysv_ipc module. Here’s how I did it --

PyObject *
SharedMemory_attach(SharedMemory *self, PyObject *args) {
    PyObject *py_address = NULL;
    void *address = NULL;
    int flags = 0;
    if (!PyArg_ParseTuple(args, "|Oi", &py_address, &flags))
        goto error_return;

    if ((!py_address) || (py_address == Py_None))
        address = NULL;
    else {
        if (PyLong_Check(py_address))
            address = PyLong_AsVoidPtr(py_address);
        else {
            PyErr_SetString(PyExc_TypeError, "address must be a long");
            goto error_return;

    // You should now be able to cast address as needed.


That code is pulled from memory.c in this module:

I don’t think I invented that technique myself. I think someone on a mailing list (perhaps this one) gave me the idea. 

Hope this helps

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