Everywhere, I can easily find an example about writing a method with Python C Extensions and use it in Python. Like this one: Python 3 extension example
$ python3
>>> import hello
>>> hello.hello_world()
Hello, world!
>>> hello.hello('world')
Hello, world!
How to do write a hello word full featured Python class (not just a module method)?
I think this How to wrap a C++ object using pure Python Extension API (python3)? question has an example, but it does not seem minimal as he is using (or wrapping?) C++ classes on it.
For example:
class ClassName(object):
"""docstring for ClassName"""
def __init__(self, hello):
super().__init__()
self.hello = hello
def talk(self, world):
print( '%s %s' % ( self.hello, world ) )
What is the equivalent of this Python class example with C Extensions?
I would use it like this:
from .mycextensionsmodule import ClassName
classname = ClassName("Hello")
classname.talk( 'world!' )
# prints "Hello world!"
My goal is to write a class fully written in C for performance (all other classes in my project will be in Python, except this one). I am not looking for portability as using ctypes, neither black boxes as using Boost.Python or SWIG. Just a high-performance class purely written with Python C Extensions.
After I got this Hello word working, I can figure my self out within Python Extensive documentation:
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Answer
See also: Python instance method in C
Create the file called MANIFEST.in
include README.md include LICENSE.txt recursive-include source *.h
Create the file called setup.py
#!/usr/bin/env python3
# -*- coding: UTF-8 -*-
from setuptools import setup, Extension
__version__ = '0.1.0'
setup(
name = 'custom',
version = __version__,
package_data = {
'': [ '**.txt', '**.md', '**.py', '**.h', '**.hpp', '**.c', '**.cpp' ],
},
ext_modules = [
Extension(
name = 'custom',
sources = [
'source/custom.cpp',
],
include_dirs = ['source'],
)
],
)
Create the file called source/custom.cpp
#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include "structmember.h"
typedef struct {
PyObject_HEAD
PyObject *first; /* first name */
PyObject *last; /* last name */
int number;
} CustomObject;
static int
Custom_traverse(CustomObject *self, visitproc visit, void *arg)
{
Py_VISIT(self->first);
Py_VISIT(self->last);
return 0;
}
static int
Custom_clear(CustomObject *self)
{
Py_CLEAR(self->first);
Py_CLEAR(self->last);
return 0;
}
static void
Custom_dealloc(CustomObject *self)
{
PyObject_GC_UnTrack(self);
Custom_clear(self);
Py_TYPE(self)->tp_free((PyObject *) self);
}
static PyObject *
Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
CustomObject *self;
self = (CustomObject *) type->tp_alloc(type, 0);
if (self != NULL) {
self->first = PyUnicode_FromString("");
if (self->first == NULL) {
Py_DECREF(self);
return NULL;
}
self->last = PyUnicode_FromString("");
if (self->last == NULL) {
Py_DECREF(self);
return NULL;
}
self->number = 0;
}
return (PyObject *) self;
}
static int
Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = {"first", "last", "number", NULL};
PyObject *first = NULL, *last = NULL, *tmp;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
&first, &last,
&self->number))
return -1;
if (first) {
tmp = self->first;
Py_INCREF(first);
self->first = first;
Py_DECREF(tmp);
}
if (last) {
tmp = self->last;
Py_INCREF(last);
self->last = last;
Py_DECREF(tmp);
}
return 0;
}
static PyMemberDef Custom_members[] = {
{"number", T_INT, offsetof(CustomObject, number), 0,
"custom number"},
{NULL} /* Sentinel */
};
static PyObject *
Custom_getfirst(CustomObject *self, void *closure)
{
Py_INCREF(self->first);
return self->first;
}
static int
Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
{
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The first attribute value must be a string");
return -1;
}
Py_INCREF(value);
Py_CLEAR(self->first);
self->first = value;
return 0;
}
static PyObject *
Custom_getlast(CustomObject *self, void *closure)
{
Py_INCREF(self->last);
return self->last;
}
static int
Custom_setlast(CustomObject *self, PyObject *value, void *closure)
{
if (value == NULL) {
PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
return -1;
}
if (!PyUnicode_Check(value)) {
PyErr_SetString(PyExc_TypeError,
"The last attribute value must be a string");
return -1;
}
Py_INCREF(value);
Py_CLEAR(self->last);
self->last = value;
return 0;
}
static PyGetSetDef Custom_getsetters[] = {
{"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
"first name", NULL},
{"last", (getter) Custom_getlast, (setter) Custom_setlast,
"last name", NULL},
{NULL} /* Sentinel */
};
static PyObject *
Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
{
return PyUnicode_FromFormat("%S %S", self->first, self->last);
}
static PyMethodDef Custom_methods[] = {
{"name", (PyCFunction) Custom_name, METH_NOARGS,
"Return the name, combining the first and last name"
},
{NULL} /* Sentinel */
};
static PyTypeObject CustomType = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "custom.Custom",
.tp_doc = "Custom objects",
.tp_basicsize = sizeof(CustomObject),
.tp_itemsize = 0,
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
.tp_new = Custom_new,
.tp_init = (initproc) Custom_init,
.tp_dealloc = (destructor) Custom_dealloc,
.tp_traverse = (traverseproc) Custom_traverse,
.tp_clear = (inquiry) Custom_clear,
.tp_members = Custom_members,
.tp_methods = Custom_methods,
.tp_getset = Custom_getsetters,
};
static PyModuleDef custommodule = {
PyModuleDef_HEAD_INIT,
.m_name = "custom",
.m_doc = "Example module that creates an extension type.",
.m_size = -1,
};
PyMODINIT_FUNC
PyInit_custom(void)
{
PyObject *m;
if (PyType_Ready(&CustomType) < 0)
return NULL;
m = PyModule_Create(&custommodule);
if (m == NULL)
return NULL;
Py_INCREF(&CustomType);
PyModule_AddObject(m, "Custom", (PyObject *) &CustomType);
return m;
}
Then, to compile it and install you can run either:
pip3 install . -v python3 setup.py install
As side note from this question How to use setuptools packages and ext_modules with the same name? do not mix on the same project *.py files and Python C Extensions, i.e., use only purely C/C++, building Python C Extensions without adding packages = [ 'package_name' ] entries because they cause the Python C Extensions code run 30%, i.e., if the program would take 7 seconds to run, now with *.py files, it will take 11 seconds.
References: