如何使用C++扩展python？ - c++

多亏了this handy skeleton module，我已经用C成功扩展了python。但是我找不到用于C++的程序，尝试修复C++在编译此骨架模块时给出的错误时遇到了循环依赖问题。

如何使用C++扩展Python？

如果不需要，我宁愿不依赖Boost(或SWIP或其他库)。依赖是一种痛苦。最好的情况是，我找到一个已经用C++编译的框架文件。

这是我为C++制作的经过编辑的骨架:

#include <Python.h>

#include "Flp.h"

static PyObject * ErrorObject;

typedef struct {
    PyObject_HEAD
    PyObject * x_attr; // attributes dictionary
} FlpObject;

static void Flp_dealloc(FlpObject * self);
static PyObject * Flp_getattr(FlpObject * self, char * name);
static int Flp_setattr(FlpObject * self, char * name, PyObject * v);
DL_EXPORT(void) initflp();

static PyTypeObject Flp_Type = {
    /* The ob_type field must be initialized in the module init function
     * to be portable to Windows without using C++. */
    PyObject_HEAD_INIT(NULL)
    0,          /*ob_size*/
    "Flp",          /*tp_name*/
    sizeof(FlpObject),  /*tp_basicsize*/
    0,          /*tp_itemsize*/
    /* methods */
    (destructor)Flp_dealloc, /*tp_dealloc*/
    0,          /*tp_print*/
    (getattrfunc)Flp_getattr, /*tp_getattr*/
    (setattrfunc)Flp_setattr, /*tp_setattr*/
    0,          /*tp_compare*/
    0,          /*tp_repr*/
    0,          /*tp_as_number*/
    0,          /*tp_as_sequence*/
    0,          /*tp_as_mapping*/
    0,          /*tp_hash*/
};

#define FlpObject_Check(v) ((v)->ob_type == &Flp_Type)

static FlpObject * newFlpObject(PyObject * arg)
{
    FlpObject * self;
    self = PyObject_NEW(FlpObject, &Flp_Type);
    if (self == NULL)
        return NULL;
    self->x_attr = NULL;
    return self;
}

// Flp methods

static void Flp_dealloc(FlpObject * self)
{
    Py_XDECREF(self->x_attr);
    PyMem_DEL(self);
}

static PyObject * Flp_demo(FlpObject * self, PyObject * args)
{
    if (! PyArg_ParseTuple(args, ""))
        return NULL;
    Py_INCREF(Py_None);
    return Py_None;
}

static PyMethodDef Flp_methods[] = {
    {"demo",    (PyCFunction)Flp_demo,  1},
    {NULL,      NULL} // sentinel
};

static PyObject * Flp_getattr(FlpObject * self, char * name)
{
    if (self->x_attr != NULL) {
        PyObject * v = PyDict_GetItemString(self->x_attr, name);
        if (v != NULL) {
            Py_INCREF(v);
            return v;
        }
    }
    return Py_FindMethod(Flp_methods, (PyObject *)self, name);
}

static int Flp_setattr(FlpObject * self, char * name, PyObject * v)
{
    if (self->x_attr == NULL) {
        self->x_attr = PyDict_New();
        if (self->x_attr == NULL)
            return -1;
    }
    if (v == NULL) {
        int rv = PyDict_DelItemString(self->x_attr, name);
        if (rv < 0)
            PyErr_SetString(PyExc_AttributeError,
                    "delete non-existing Flp attribute");
        return rv;
    }
    else
        return PyDict_SetItemString(self->x_attr, name, v);
}
/* --------------------------------------------------------------------- */

/* Function of two integers returning integer */

static PyObject * flp_foo(PyObject * self, PyObject * args)
{
    long i, j;
    long res;
    if (!PyArg_ParseTuple(args, "ll", &i, &j))
        return NULL;
    res = i+j; /* flpX Do something here */
    return PyInt_FromLong(res);
}


/* Function of no arguments returning new Flp object */

static PyObject * flp_new(PyObject * self, PyObject * args)
{
    FlpObject *rv;

    if (!PyArg_ParseTuple(args, ""))
        return NULL;
    rv = newFlpObject(args);
    if ( rv == NULL )
        return NULL;
    return (PyObject *)rv;
}

/* Example with subtle bug from extensions manual ("Thin Ice"). */

static PyObject * flp_bug(PyObject * self, PyObject * args)
{
    PyObject *list, *item;

    if (!PyArg_ParseTuple(args, "O", &list))
        return NULL;

    item = PyList_GetItem(list, 0);
    /* Py_INCREF(item); */
    PyList_SetItem(list, 1, PyInt_FromLong(0L));
    PyObject_Print(item, stdout, 0);
    printf("\n");
    /* Py_DECREF(item); */

    Py_INCREF(Py_None);
    return Py_None;
}

/* Test bad format character */

static PyObject * flp_roj(PyObject * self, PyObject * args)
{
    PyObject *a;
    long b;
    if (!PyArg_ParseTuple(args, "O#", &a, &b))
        return NULL;
    Py_INCREF(Py_None);
    return Py_None;
}


/* List of functions defined in the module */

static PyMethodDef flp_methods[] = {
    {"roj",     flp_roj,     1},
    {"foo",     flp_foo,     1},
    {"new",     flp_new,     1},
    {"bug",     flp_bug,     1},
    {NULL,      NULL}       /* sentinel */
};


/* Initialization function for the module (*must* be called initflp) */

DL_EXPORT(void) initflp()
{
    PyObject *m, *d;

    /* Initialize the type of the new type object here; doing it here
     * is required for portability to Windows without requiring C++. */
    Flp_Type.ob_type = &PyType_Type;

    /* Create the module and add the functions */
    m = Py_InitModule("flp", flp_methods);

    /* Add some symbolic constants to the module */
    d = PyModule_GetDict(m);
    ErrorObject = PyErr_NewException("flp.error", NULL, NULL);
    PyDict_SetItemString(d, "error", ErrorObject);
}

这对我来说编译很好，但是当我测试它时:

$ python
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import flp
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dynamic module does not define init function (initflp)
>>>

参考方案

首先，即使您不想引入其他依赖关系，我也建议您看一下PyCXX。引用其网页:

CXX / Objects是一组C++工具，可简化编写Python扩展的过程。 PyCXX使编写Python扩展更容易的主要方式是，它大大增加了程序不会产生引用计数错误并且不必不断检查来自Python C API的错误返回的可能性。 CXX / Objects通过以下方式将Python与C++集成:

依靠C++异常处理来检测错误和清除。在复杂的函数中，这在用C编写时通常是一个巨大的问题。使用PyCXX，我们可以让编译器跟踪发生错误时需要取消引用的对象。

标准模板库(STL)及其许多算法可与Python容器(如列表和元组)即插即用。

可选的CXX / Extensions工具允许您将笨拙的C表替换为定义模块和扩展对象的对象和方法调用。

我认为PyCXX是在BSD许可下获得许可的，这意味着如果您的扩展将以类似的许可发布，那么您也可以在扩展的分布式tarball中包含PyCXX的整个源代码。
如果您确实绝对不想依赖PyCXX或任何其他第三方库，我认为您只需要wrap函数，Python解释器将在extern "C" {和}中调用这些函数，以避免名称混乱。
这是更正的代码:

#include <Python.h>

#include "Flp.h"

static PyObject * ErrorObject;

typedef struct {
    PyObject_HEAD
    PyObject * x_attr; // attributes dictionary
} FlpObject;

extern "C" {
    static void Flp_dealloc(FlpObject * self);
    static PyObject * Flp_getattr(FlpObject * self, char * name);
    static int Flp_setattr(FlpObject * self, char * name, PyObject * v);
    DL_EXPORT(void) initflp();
}

static PyTypeObject Flp_Type = {
    /* The ob_type field must be initialized in the module init function
     * to be portable to Windows without using C++. */
    PyObject_HEAD_INIT(NULL)
    0,          /*ob_size*/
    "Flp",          /*tp_name*/
    sizeof(FlpObject),  /*tp_basicsize*/
    0,          /*tp_itemsize*/
    /* methods */
    (destructor)Flp_dealloc, /*tp_dealloc*/
    0,          /*tp_print*/
    (getattrfunc)Flp_getattr, /*tp_getattr*/
    (setattrfunc)Flp_setattr, /*tp_setattr*/
    0,          /*tp_compare*/
    0,          /*tp_repr*/
    0,          /*tp_as_number*/
    0,          /*tp_as_sequence*/
    0,          /*tp_as_mapping*/
    0,          /*tp_hash*/
};

#define FlpObject_Check(v) ((v)->ob_type == &Flp_Type)

static FlpObject * newFlpObject(PyObject * arg)
{
    FlpObject * self;
    self = PyObject_NEW(FlpObject, &Flp_Type);
    if (self == NULL)
        return NULL;
    self->x_attr = NULL;
    return self;
}

// Flp methods

static void Flp_dealloc(FlpObject * self)
{
    Py_XDECREF(self->x_attr);
    PyMem_DEL(self);
}

static PyObject * Flp_demo(FlpObject * self, PyObject * args)
{
    if (! PyArg_ParseTuple(args, ""))
        return NULL;
    Py_INCREF(Py_None);
    return Py_None;
}

static PyMethodDef Flp_methods[] = {
    {"demo",    (PyCFunction)Flp_demo,  1},
    {NULL,      NULL} // sentinel
};

static PyObject * Flp_getattr(FlpObject * self, char * name)
{
    if (self->x_attr != NULL) {
        PyObject * v = PyDict_GetItemString(self->x_attr, name);
        if (v != NULL) {
            Py_INCREF(v);
            return v;
        }
    }
    return Py_FindMethod(Flp_methods, (PyObject *)self, name);
}

static int Flp_setattr(FlpObject * self, char * name, PyObject * v)
{
    if (self->x_attr == NULL) {
        self->x_attr = PyDict_New();
        if (self->x_attr == NULL)
            return -1;
    }
    if (v == NULL) {
        int rv = PyDict_DelItemString(self->x_attr, name);
        if (rv < 0)
            PyErr_SetString(PyExc_AttributeError,
                    "delete non-existing Flp attribute");
        return rv;
    }
    else
        return PyDict_SetItemString(self->x_attr, name, v);
}
/* --------------------------------------------------------------------- */

/* Function of two integers returning integer */

static PyObject * flp_foo(PyObject * self, PyObject * args)
{
    long i, j;
    long res;
    if (!PyArg_ParseTuple(args, "ll", &i, &j))
        return NULL;
    res = i+j; /* flpX Do something here */
    return PyInt_FromLong(res);
}


/* Function of no arguments returning new Flp object */

static PyObject * flp_new(PyObject * self, PyObject * args)
{
    FlpObject *rv;
    
    if (!PyArg_ParseTuple(args, ""))
        return NULL;
    rv = newFlpObject(args);
    if ( rv == NULL )
        return NULL;
    return (PyObject *)rv;
}

/* Example with subtle bug from extensions manual ("Thin Ice"). */

static PyObject * flp_bug(PyObject * self, PyObject * args)
{
    PyObject *list, *item;
    
    if (!PyArg_ParseTuple(args, "O", &list))
        return NULL;
    
    item = PyList_GetItem(list, 0);
    /* Py_INCREF(item); */
    PyList_SetItem(list, 1, PyInt_FromLong(0L));
    PyObject_Print(item, stdout, 0);
    printf("\n");
    /* Py_DECREF(item); */
    
    Py_INCREF(Py_None);
    return Py_None;
}

/* Test bad format character */

static PyObject * flp_roj(PyObject * self, PyObject * args)
{
    PyObject *a;
    long b;
    if (!PyArg_ParseTuple(args, "O#", &a, &b))
        return NULL;
    Py_INCREF(Py_None);
    return Py_None;
}


/* List of functions defined in the module */

static PyMethodDef flp_methods[] = {
    {"roj",     flp_roj,     1},
    {"foo",     flp_foo,     1},
    {"new",     flp_new,     1},
    {"bug",     flp_bug,     1},
    {NULL,      NULL}       /* sentinel */
};


/* Initialization function for the module (*must* be called initflp) */

DL_EXPORT(void) initflp()
{
    PyObject *m, *d;

    /* Initialize the type of the new type object here; doing it here
     * is required for portability to Windows without requiring C++. */
    Flp_Type.ob_type = &PyType_Type;

    /* Create the module and add the functions */
    m = Py_InitModule("flp", flp_methods);

    /* Add some symbolic constants to the module */
    d = PyModule_GetDict(m);
    ErrorObject = PyErr_NewException("flp.error", NULL, NULL);
    PyDict_SetItemString(d, "error", ErrorObject);
}

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