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Date: Sun, 15 Jan 2012 01:37:22 -0600
From: Evan Driscoll <edriscoll@wisc.edu>
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Subject: Extension module question
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As I hinted at in an earlier email, I'm working on a module which will
allow calling readdir() (and FindFirstFile on Windows, hopefully pretty
uniformly) from Python. The responses I got convinced me that it was a
good idea to write a C-to-Python bridge as an extension module.

What I'm not sure about is how to store pointers to *C* stuff between
calls. In particular, opendir() returns a DIR* which you then need to
pass to calls to readdir() in the future (and closedir()).

So I've got this:

    static PyObject*
    py_opendir(PyObject* self, PyObject* args)
    {
        const char* dirname =3D 0;
        if (!PyArg_ParseTuple(args, "s", &dirname)) {
            return NULL;
        }
        // Eventually want to Py_BEGIN_ALLOW_THREADS here
        DIR* directory =3D
opendir(dirname);                                                   =20

        PyObject out =3D PyBuildValue( ???, directory );
        return out;
    }

but I don't know what to build. (I might want to wrap it in a custom
handle class or something, but I still need to know how to build the
value I eventually store in an attribute of that class.)

My best idea is to use an unsigned long (so "k") and add a static
assertion that sizeof(long)=3D=3Dsizeof(void*). Is this the canonical way=
 of
doing something like this, or am I missing a better way?

Evan



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