如何使用纯Python扩展API（python3）包装C ++对象？ [英] How to wrap a C++ object using pure Python Extension API (python3)?

问题描述

我想知道如何使用 Python扩展API 包装C ++对象（和distutils），而无需外部工具（例如Cython，Boost，SWIG等）。

请注意，我的C ++对象具有内存分配，因此必须调用析构函数以避免内存泄漏。

  #include Voice.h 
 
命名空间转换
 {
 Voice :: Voice（int fftSize）{mem = new double [fftSize]; } 
 
 Voice ::〜Voice（）{delete [] mem; } 
 
 int Voice :: method1（）{/ *做东西* / return（1）; } 
} 
  

我只想在Python中做类似的事情：

 导入声音
 
v = voice.Voice（512）
 result = v.method1（）
  

解决方案

似乎答案实际上在这里： https://docs.python.org/3.6/extending/newtypes.html

通过示例，但并非一帆风顺。

编辑1：

<实际上，并不是将C ++对象包装在Python对象中，而是用C代码创建一个Python对象。 （edit2：所以您可以包装C ++对象！）

编辑2：

以下是使用 Python新类型

。

原始C ++文件： Voice.cpp

  #include< cstdio> 
 
 #include Voice.h 
 
命名空间转换
 {
 Voice :: Voice（int fftSize）{
 printf（ c ++ voice\n的构造函数）； 
 this-> fftSize = fftSize; 
 mem = new double [fftSize]; 
} 
 
 Voice ::〜Voice（）{delete [] mem; } 
 
 int语音:: filter（int freq）{
 printf（ c ++语音过滤方法\n）; 
 return（doubleIt（3））; 
} 
 int语音:: doubleIt（int i）{return 2 * i; } 
} 
  

。

原始h文件： Voice.h

 命名空间转换{
 
 class Voice {
 public：
 double * mem; 
 int fftSize; 
 
 Voice（int fftSize）; 
〜Voice（）; 
 
 int过滤器（int freq）; 
 int doubleIt（int i）; 
}; 
 
} 
  

。

C ++ Python包装文件：voiceWrapper.cpp

  #include< Python.h> 
 
 #include< cstdio> 
 //〜#include structmember.h 
 
 #include Voice.h 
 
使用transform :: Voice; 
 
 typedef struct {
 PyObject_HEAD 
 Voice * ptrObj; 
} PyVoice; 
 
 
 
 
静态PyModuleDef语音模块= {
 PyModuleDef_HEAD_INIT，
 voice，
包装了C ++的示例模块对象，
 -1，
 NULL，NULL，NULL，NULL，NULL 
}; 
 
 static int PyVoice_init（PyVoice * self，PyObject * args，PyObject * kwds）
 //初始化PyVoice对象
 {
 int fftSize; 
 
 if（！PyArg_ParseTuple（args， i，& fftSize））
返回-1; 
 
 self-> ptrObj =新语音（fftSize）; 
 
返回0; 
} 
 
 static void PyVoice_dealloc（PyVoice * self）
 //破坏对象
 {
 delete self-> ptrObj; 
 Py_TYPE（self）-> tp_free（self）; 
} 
 
 
静态PyObject * PyVoice_filter（PyVoice * self，PyObject * args）
 {
 int freq; 
 int retval; 
 
 if（！PyArg_ParseTuple（args， i，& freq））
返回Py_False; 
 
 retval =（self-> ptrObj）-> filter（freq）; 
 
返回Py_BuildValue（ i，retval）; 
} 
 
 
静态PyMethodDef PyVoice_methods [] = {
 { filter，（PyCFunction）PyVoice_filter，METH_VARARGS， filter the mem voice}，
 {NULL} / *前哨* / 
}; 
 
静态PyTypeObject PyVoiceType = {PyVarObject_HEAD_INIT（NULL，0）
 voice.Voice / * tp_name * / 
}; 
 
 
 PyMODINIT_FUNC PyInit_voice（void）
 //创建模块
 {
 PyObject * m; 
 
 PyVoiceType.tp_new = PyType_GenericNew; 
 PyVoiceType.tp_basicsize = sizeof（PyVoice）; 
 PyVoiceType.tp_dealloc =（析构函数）PyVoice_dealloc; 
 PyVoiceType.tp_flags = Py_TPFLAGS_DEFAULT; 
 PyVoiceType.tp_doc =语音对象; 
 PyVoiceType.tp_methods = PyVoice_methods; 
 //〜PyVoiceType.tp_members = Noddy_members; 
 PyVoiceType.tp_init =（initproc）PyVoice_init; 
 
如果（PyType_Ready（& PyVoiceType）< 0）
返回NULL; 
 
 m = PyModule_Create（& voicemodule）; 
 if（m == NULL）
返回NULL; 
 
 Py_INCREF（& PyVoiceType）; 
 PyModule_AddObject（m， Voice，（PyObject *）& PyVoiceType）; //将语音对象添加到模块
 return m;中。 
} 
  

。

distutils文件：distutils.core导入设置中的 setup.py

 ，扩展
 
 setup（name ='voicePkg'，version ='1.0'，\ 
 ext_modules = [Extension（'voice'，['voiceWrapper.cpp'，'Voice.cpp' ]）]）
  

。

python测试文件： test.py

 导入声音
 
v = voice.Voice（512）
 result = v.filter（5）
 print（'result ='+ str（result））
  

。

和魔术：

  sudo python3 setup.py install 
 python3 test.py 
  

输出为：

  c ++语音构造函数
 c ++语音过滤器方法
 result = 6 
  

享受！

Doom

I want to know how to wrap a C++ object with Python Extension API (and distutils) without external tools (like Cython, Boost, SWIG, ...). Just in pure Python way without creating a dll.

Note that my C++ object has memory allocations so destructor has to be called to avoid memory leaks.

#include "Voice.h"

namespace transformation
{ 
  Voice::Voice(int fftSize) { mem=new double[fftSize]; } 

  Voice::~Voice() { delete [] mem; } 

  int Voice::method1() { /*do stuff*/ return (1); } 
}

I just want to do somethings like that in Python :

import voice

v=voice.Voice(512)
result=v.method1()

解决方案

Seems that the answer was in fact here : https://docs.python.org/3.6/extending/newtypes.html

With examples, but not really easy.

EDIT 1 :

In fact, it is not really for wrapping a C++ object in a Python object, but rather to create a Python object with C code. (edit2 : and so you can wrap C++ object!)

EDIT 2 :

Here is a solution using the Python newtypes

.

Original C++ file : Voice.cpp

#include <cstdio>

#include "Voice.h"

namespace transformation
{ 
    Voice::Voice(int fftSize) {
        printf("c++ constructor of voice\n");
        this->fftSize=fftSize;
        mem=new double[fftSize];
        } 

    Voice::~Voice() { delete [] mem; } 

    int Voice::filter(int freq) {
        printf("c++ voice filter method\n");
        return (doubleIt(3));
    }
    int Voice::doubleIt(int i) { return 2*i; }
}

.

Original h file : Voice.h

namespace transformation {

    class Voice {
    public:
        double *mem;
        int fftSize;

        Voice(int fftSize);
        ~Voice();

        int filter(int freq);
        int doubleIt(int i);
    };

}

.

C++ Python wrapper file : voiceWrapper.cpp

#include <Python.h>

#include <cstdio>
//~ #include "structmember.h"

#include "Voice.h"

using transformation::Voice;

typedef struct {
    PyObject_HEAD
    Voice * ptrObj;
} PyVoice;




static PyModuleDef voicemodule = {
    PyModuleDef_HEAD_INIT,
    "voice",
    "Example module that wrapped a C++ object",
    -1,
    NULL, NULL, NULL, NULL, NULL
};

static int PyVoice_init(PyVoice *self, PyObject *args, PyObject *kwds)
// initialize PyVoice Object
{
    int fftSize;

    if (! PyArg_ParseTuple(args, "i", &fftSize))
        return -1;

    self->ptrObj=new Voice(fftSize);

    return 0;
}

static void PyVoice_dealloc(PyVoice * self)
// destruct the object
{
    delete self->ptrObj;
    Py_TYPE(self)->tp_free(self);
}


static PyObject * PyVoice_filter(PyVoice* self, PyObject* args)
{
    int freq;
    int retval;

    if (! PyArg_ParseTuple(args, "i", &freq))
        return Py_False;

    retval = (self->ptrObj)->filter(freq);

    return Py_BuildValue("i",retval);
}


static PyMethodDef PyVoice_methods[] = {
    { "filter", (PyCFunction)PyVoice_filter,    METH_VARARGS,       "filter the mem voice" },
    {NULL}  /* Sentinel */
};

static PyTypeObject PyVoiceType = { PyVarObject_HEAD_INIT(NULL, 0)
                                    "voice.Voice"   /* tp_name */
                                };


PyMODINIT_FUNC PyInit_voice(void)
// create the module
{
    PyObject* m;

    PyVoiceType.tp_new = PyType_GenericNew;
    PyVoiceType.tp_basicsize=sizeof(PyVoice);
    PyVoiceType.tp_dealloc=(destructor) PyVoice_dealloc;
    PyVoiceType.tp_flags=Py_TPFLAGS_DEFAULT;
    PyVoiceType.tp_doc="Voice objects";
    PyVoiceType.tp_methods=PyVoice_methods;
    //~ PyVoiceType.tp_members=Noddy_members;
    PyVoiceType.tp_init=(initproc)PyVoice_init;

    if (PyType_Ready(&PyVoiceType) < 0)
        return NULL;

    m = PyModule_Create(&voicemodule);
    if (m == NULL)
        return NULL;

    Py_INCREF(&PyVoiceType);
    PyModule_AddObject(m, "Voice", (PyObject *)&PyVoiceType); // Add Voice object to the module
    return m;
}

.

distutils file : setup.py

from distutils.core import setup, Extension

setup(name='voicePkg', version='1.0',  \
      ext_modules=[Extension('voice', ['voiceWrapper.cpp','Voice.cpp'])])

.

python test file : test.py

import voice

v=voice.Voice(512)
result=v.filter(5)
print('result='+str(result))

.

and magic :

sudo python3 setup.py install
python3 test.py

Output is :

c++ constructor of voice
c++ voice filter method
result=6

Enjoy !

Doom

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