Python ctypes: Python file object <-> C FILE *

Question

I am using ctypes to wrap a C-library (which I have control over) with Python. I want to wrap a C-function with declaration:

int fread_int( FILE * stream );
         


        

Answer 1

Well;

I tried the fileno based solution, but was quite uncomfortable with opening the file twice; It was also not clear to me how to avoid the return value from fdopen() to leak.

In the end I wrote a microscopic C-extension:

static PyObject cfile(PyObject * self, PyObject * args) {
    PyObject * pyfile;
    if (PyArg_ParseTuple( 'O' , &pyfile)) {
       FILE * cfile = PyFile_AsFile( pyfile );
       return Py_BuildValue( "l" , cfile );
    else
        return Py_BuildValue( "" );
}

which uses PyFile_AsFile and subsequently returns the FILE * pointer as a pure pointer value to Python which passes this back to C function expecting FILE * input. It works at least.

Joakim