From philip at semanchuk.com  Sat Apr  5 20:12:00 2014
From: philip at semanchuk.com (Philip Semanchuk)
Date: Sat, 5 Apr 2014 14:12:00 -0400
Subject: [capi-sig] (no subject)
In-Reply-To: <CAE-iVQh72nkf+VbA8gSU6s+PfxwUBjq-A-TarpXPaDf+sXhY2Q@mail.gmail.com>
References: <CAE-iVQh72nkf+VbA8gSU6s+PfxwUBjq-A-TarpXPaDf+sXhY2Q@mail.gmail.com>
Message-ID: <48EF9A46-7F41-4646-8C1C-5580DBBD5095@semanchuk.com>


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:
http://semanchuk.com/philip/sysv_ipc/

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
Philip