Python C API cheatsheet¶
PyObject header¶
// ref: python source code
// Python/Include/object.c
#define _PyObject_HEAD_EXTRA \
struct _object *_ob_next;\
struct _object *_ob_prev;
#define PyObject_HEAD \
_PyObject_HEAD_EXTRA \
Py_ssize_t ob_refcnt;\
struct _typeobject *ob_type;
Python C API Template¶
C API source¶
#include <Python.h>
typedef struct {
PyObject_HEAD
} spamObj;
static PyTypeObject spamType = {
PyObject_HEAD_INIT(&PyType_Type)
0, //ob_size
"spam.Spam", //tp_name
sizeof(spamObj), //tp_basicsize
0, //tp_itemsize
0, //tp_dealloc
0, //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_DEFAULT, //tp_flags
"spam objects", //tp_doc
};
static PyMethodDef spam_methods[] = {
{NULL} /* Sentinel */
};
/* declarations for DLL import */
#ifndef PyMODINIT_FUNC
#define PyMODINIT_FUNC void
#endif
PyMODINIT_FUNC
initspam(void)
{
PyObject *m;
spamType.tp_new = PyType_GenericNew;
if (PyType_Ready(&spamType) < 0) {
goto END;
}
m = Py_InitModule3("spam", spam_methods, "Example of Module");
Py_INCREF(&spamType);
PyModule_AddObject(m, "spam", (PyObject *)&spamType);
END:
return;
}
Prepare setup.py¶
from distutils.core import setup
from distutils.core import Extension
setup(name="spam",
version="1.0",
ext_modules=[Extension("spam", ["spam.c"])])
Build C API source¶
$ python setup.py build
$ python setup.py install
Run the C module¶
>>> import spam
>>> spam.__doc__
'Example of Module'
>>> spam.spam
<type 'spam.Spam'>
PyObject with Member and Methods¶
C API source¶
#include <Python.h>
#include <structmember.h>
typedef struct {
PyObject_HEAD
PyObject *hello;
PyObject *world;
int spam_id;
} spamObj;
static void
spamdealloc(spamObj *self)
{
Py_XDECREF(self->hello);
Py_XDECREF(self->world);
self->ob_type
->tp_free((PyObject*)self);
}
/* __new__ */
static PyObject *
spamNew(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
spamObj *self = NULL;
self = (spamObj *)
type->tp_alloc(type, 0);
if (self == NULL) {
goto END;
}
/* alloc str to hello */
self->hello =
PyString_FromString("");
if (self->hello == NULL)
{
Py_XDECREF(self);
self = NULL;
goto END;
}
/* alloc str to world */
self->world =
PyString_FromString("");
if (self->world == NULL)
{
Py_XDECREF(self);
self = NULL;
goto END;
}
self->spam_id = 0;
END:
return (PyObject *)self;
}
/* __init__ */
static int
spamInit(spamObj *self, PyObject *args, PyObject *kwds)
{
int ret = -1;
PyObject *hello=NULL,
*world=NULL,
*tmp=NULL;
static char *kwlist[] = {
"hello",
"world",
"spam_id", NULL};
/* parse input arguments */
if (! PyArg_ParseTupleAndKeywords(
args, kwds,
"|OOi",
kwlist,
&hello, &world,
&self->spam_id)) {
goto END;
}
/* set attr hello */
if (hello) {
tmp = self->hello;
Py_INCREF(hello);
self->hello = hello;
Py_XDECREF(tmp);
}
/* set attr world */
if (world) {
tmp = self->world;
Py_INCREF(world);
self->world = world;
Py_XDECREF(tmp);
}
ret = 0;
END:
return ret;
}
static long
fib(long n) {
if (n<=2) {
return 1;
}
return fib(n-1)+fib(n-2);
}
static PyObject *
spamFib(spamObj *self, PyObject *args)
{
PyObject *ret = NULL;
long arg = 0;
if (!PyArg_ParseTuple(args, "i", &arg)) {
goto END;
}
ret = PyInt_FromLong(fib(arg));
END:
return ret;
}
//ref: python doc
static PyMemberDef spam_members[] = {
/* spameObj.hello*/
{"hello", //name
T_OBJECT_EX, //type
offsetof(spamObj, hello), //offset
0, //flags
"spam hello"}, //doc
/* spamObj.world*/
{"world",
T_OBJECT_EX,
offsetof(spamObj, world),
0,
"spam world"},
/* spamObj.spam_id*/
{"spam_id",
T_INT,
offsetof(spamObj, spam_id),
0,
"spam id"},
/* Sentiel */
{NULL}
};
static PyMethodDef spam_methods[] = {
/* fib */
{"spam_fib",
(PyCFunction)spamFib,
METH_VARARGS,
"Calculate fib number"},
/* Sentiel */
{NULL}
};
static PyMethodDef module_methods[] = {
{NULL} /* Sentinel */
};
static PyTypeObject spamKlass = {
PyObject_HEAD_INIT(NULL)
0, //ob_size
"spam.spamKlass", //tp_name
sizeof(spamObj), //tp_basicsize
0, //tp_itemsize
(destructor) spamdealloc, //tp_dealloc
0, //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_DEFAULT |
Py_TPFLAGS_BASETYPE, //tp_flags
"spamKlass objects", //tp_doc
0, //tp_traverse
0, //tp_clear
0, //tp_richcompare
0, //tp_weaklistoffset
0, //tp_iter
0, //tp_iternext
spam_methods, //tp_methods
spam_members, //tp_members
0, //tp_getset
0, //tp_base
0, //tp_dict
0, //tp_descr_get
0, //tp_descr_set
0, //tp_dictoffset
(initproc)spamInit, //tp_init
0, //tp_alloc
spamNew, //tp_new
};
/* declarations for DLL import */
#ifndef PyMODINIT_FUNC
#define PyMODINIT_FUNC void
#endif
PyMODINIT_FUNC
initspam(void)
{
PyObject* m;
if (PyType_Ready(&spamKlass) < 0) {
goto END;
}
m = Py_InitModule3(
"spam", // Mod name
module_methods, // Mod methods
"Spam Module"); // Mod doc
if (m == NULL) {
goto END;
}
Py_INCREF(&spamKlass);
PyModule_AddObject(
m, // Module
"SpamKlass", // Class Name
(PyObject *) &spamKlass); // Class
END:
return;
}
Compare performance with pure Python¶
>>> import spam
>>> o = spam.SpamKlass()
>>> def profile(func):
... def wrapper(*args, **kwargs):
... s = time.time()
... ret = func(*args, **kwargs)
... e = time.time()
... print e-s
... return wrapper
...
>>> def fib(n):
... if n <= 2:
... return n
... return fib(n-1)+fib(n-2)
...
>>> @profile
... def cfib(n):
... o.spam_fib(n)
...
>>> @profile
... def pyfib(n):
... fib(n)
...
>>> cfib(30)
0.0106310844421
>>> pyfib(30)
0.399799108505
