I think I may have figured all this out by looking at examples in the
python source, e.g. xxsubtype.c etc. Nonetheless, I would appreciate
any extra info others might provide.
Thanks again.
--ralph
Ralph Butler wrote:
> Hi:
> I have a question about extending python with C. I have read the docs
> and done some googling, but come up short on this particular (small)
> problem. I want to write a c extension to int. In particular, I want
> to grab the memory for the int from an alternative heap. I am confused
> about 2 things: (1) Do I need to call the __init__ function for int
> itself, and if so, how do I do that? (2) Do I supply my own tp_alloc
> function to retrieve the memory for my new elements, and if so, what
> should it look like? (Assume for the moment that I simply plan to do a
> malloc.)
>
> I have attached code that does most of the work and has my initials
> (RMB) at a couple of the pieces of code I think I may need.
>
> Any pointers to fairly specific examples would be appreciated. I have
> found non-specific examples a bit confusing.
>
> Thanks.
> --ralph
>
>
> ------------------------------------------------------------------------
>
> from distutils.core import setup, Extension
>
> setup (name = "intext",
> version = "1.0",
> maintainer = "rbutler",
> maintainer_email = "[EMAIL PROTECTED]",
> description = "shared memory objects",
> ext_modules = [Extension('intext',sources=['intext.c'])]
> )
>
>
> ------------------------------------------------------------------------
>
> #!/usr/bin/env python
>
> # inherit from int
>
> import intext
>
> x = intext.INTEXT(44)
> print type(x)
> print x
> print int(x) + 33
>
>
> ------------------------------------------------------------------------
>
> #include <Python.h>
>
> static PyTypeObject *INTEXT_type_p;
>
> #define PyINTEXT_Check(obj) ((obj)->ob_type == INTEXT_type_p)
>
> typedef struct newtypeobjectstruct
> {
> PyObject_HEAD
> int *intextp;
> } pyintext;
>
> static PyObject *pyintext_tp_alloc(PyTypeObject *type, int nitems)
> {
> printf("tpalloc: nitems=%d\n",nitems);
> // RMB: grab memory for the object
> return (PyObject *) NULL;
> }
>
> static int pyintext_init(pyintext *self, PyObject *args)
> {
> int iv;
>
> if ( ! PyArg_ParseTuple(args,"i",&iv))
> return -1;
> printf("init iv=%d\n",iv);
> // RMB: invoke the super class __init__ ??
> return 0;
> }
>
> static char INTEXT_type_doc[] = "intext type doc";
> PyTypeObject INTEXTType = {
> PyObject_HEAD_INIT(&PyType_Type) 0, /* ob_size */
> "intext.INTEXT", /* tp_name */
> sizeof(pyintext), /* tp_basicsize */
> 0, /* tp_itemsize */
> 0, /* tp_dealloc */
> (printfunc) NULL, /* tp_print */
> 0, /* tp_getattr*/
> 0, /* tp_setattr */
> 0, /* tp_compare */
> 0, /* tp_repr */
> 0, /* tp_as_number */
> 0, /* tp_as_sequence */
> 0, /* tp_as_mapping */
> 0, /* tp_hash */
> 0, /* tp_call */
> 0, /* tp_str */
> 0, /* tp_getattro */
> 0, /* tp_setattro */
> 0, /* tp_as_buffer */
> Py_TPFLAGS_HAVE_CLASS, /* tp_flags */
> INTEXT_type_doc, /* tp_doc */
> 0, /* tp_traverse */
> 0, /* tp_clear */
> 0, /* tp_richcompare */
> 0, /* tp_weaklistoffset */
> 0, /* tp_iter */
> 0, /* tp_iternext */
> 0, /* tp_methods */
> 0, /* tp_members */
> 0, /* tp_getset */
> &PyInt_Type, /* tp_base */
> 0, /* tp_dict */
> 0, /* tp_descr_get */
> 0, /* tp_descr_set */
> 0, /* tp_dictoffset */
> (initproc) pyintext_init, /* tp_init */
> pyintext_tp_alloc, /* tp_alloc */
> PyType_GenericNew, /* tp_new */
> 0, /* tp_free */
> 0, /* tp_is_gc */
> };
>
> static char intext_module_doc[] = "intext module doc";
> static struct PyMethodDef intext_module_methods[] = {
> {NULL, NULL, 0, NULL}
> };
>
> void initintext(void)
> {
> PyObject *m;
> /* Create the module and add the functions */
> INTEXT_type_p = &INTEXTType;
> INTEXTType.ob_type = &PyType_Type;
>
> if (PyType_Ready(INTEXT_type_p) < 0)
> return;
>
> m = Py_InitModule3("intext",intext_module_methods,intext_module_doc);
> if (!m)
> {
> printf("Py_InitModule3 failed\n");
> return;
> }
>
> Py_INCREF(INTEXT_type_p);
> PyModule_AddObject(m, "INTEXT", (PyObject *) & INTEXTType);
> }
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