Python Cookbook

Coding the Methods of a Python Class in C

Credit: Brent Burley

Problem

You have a Python class and want to recode it as a C extension for speed while keeping all client-code unchanged, so it must remain a class.

Solution

One hardly ever sees Python class objects built in C extensions. And yet it’s anything but difficult, and, in fact, it’s quite handy:

#include <Python.h>

static PyObject* Foo_init(PyObject *self, PyObject *args)
{
    printf("Foo._ _init_ _ called\n");
    Py_INCREF(Py_None);
    return Py_None;
}

static PyObject* Foo_doSomething(PyObject *self, PyObject *args)
{
    printf("Foo.doSomething called\n");
    Py_INCREF(Py_None);
    return Py_None;
}

static PyMethodDef FooMethods[] =
{
    {"_ _init_ _", Foo_init, METH_VARARGS, "doc string"},
    {"doSomething", Foo_doSomething, METH_VARARGS, "doc string"},
    {0, 0},
};

static PyMethodDef ModuleMethods[] = { {0, 0} };

#ifdef _ _cplusplus
extern "C"
#endif
void initFoo(  )
{
    PyMethodDef *def;

    /* create new module and class objects */
    PyObject *module = Py_InitModule("Foo", ModuleMethods);
    PyObject *moduleDict = PyModule_GetDict(module);
    PyObject *classDict = PyDict_New(  );
    PyObject *className = PyString_FromString("Foo");
    PyObject *fooClass = PyClass_New(NULL, classDict, className);
    PyDict_SetItemString(moduleDict, "Foo", fooClass);
    Py_DECREF(classDict);
    Py_DECREF(className);
    Py_DECREF(fooClass);

    /* add methods to class */
    for (def = FooMethods; def->ml_name != NULL; def++) {
        PyObject *func = PyCFunction_New(def, NULL);
 PyObject *method = PyMethod_New(func, ...