具有可变数量参数的Python扩展模块

我试图找出在C扩展模块中如何为函数提供一个变量(也许是)相当多的参数.

阅读约PyArg_ParseTuple,似乎你必须知道有多少人接受,一些是强制的,一些是可选的,但都有自己的变量.我希望PyArg_UnpackTuple能够处理这个问题,但是当我尝试以错误的方式使用它时,它似乎只是给我总线错误.

作为一个例子,将以下可能想要制作的python代码放入扩展模块(在C中).

def hypot(*vals):
    if len(vals) !=1 :
        return math.sqrt(sum((v ** 2 for v in vals)))
    else: 
        return math.sqrt(sum((v ** 2 for v in vals[0])))

这可以用任意数量的参数调用或迭代,hypot(3,4,5),hypot([3,4,5])和hypot(* [3,4,5])都给出相同的答案.

我的C函数的开头看起来像这样

static PyObject *hypot_tb(PyObject *self, PyObject *args) {
// lots of code
// PyArg_ParseTuple or PyArg_UnpackTuple
}

许多人认为yasar11732.这里的下一个人是一个完全正常工作的扩展模块(_toolboxmodule.c),它只接受任何数字或整数参数并返回由这些参数组成的列表(名称不好).一个玩具,但说明了需要做什么.

#include <Python.h>

int ParseArguments(long arr[],Py_ssize_t size, PyObject *args) {
    /* Get arbitrary number of positive numbers from Py_Tuple */
    Py_ssize_t i;
    PyObject *temp_p, *temp_p2;

    for (i=0;i<size;i++) {
        temp_p = PyTuple_GetItem(args,i);
        if(temp_p == NULL) {return NULL;}

        /* Check if temp_p is numeric */
        if (PyNumber_Check(temp_p) != 1) {
            PyErr_SetString(PyExc_TypeError,"Non-numeric argument.");
            return NULL;
        }

        /* Convert number to python long and than C unsigned long */
        temp_p2 = PyNumber_Long(temp_p);
        arr[i] = PyLong_AsUnsignedLong(temp_p2);
        Py_DECREF(temp_p2);
    }
    return 1;
}

static PyObject *hypot_tb(PyObject *self, PyObject *args)
{
    Py_ssize_t TupleSize = PyTuple_Size(args);
    long *nums = malloc(TupleSize * sizeof(unsigned long));
    PyObject *list_out;
    int i;

    if(!TupleSize) {
        if(!PyErr_Occurred()) 
            PyErr_SetString(PyExc_TypeError,"You must supply at least one argument.");
        return NULL;
    }
    if (!(ParseArguments(nums, TupleSize, args)) { 
        free(nums);
        return NULL;
    }

    list_out = PyList_New(TupleSize);
    for(i=0;i<TupleSize;i++)
        PyList_SET_ITEM(list_out, i, PyInt_FromLong(nums[i]));
    free(nums);
    return (PyObject *)list_out;
}

static PyMethodDef toolbox_methods[] = {
   { "hypot", (PyCFunction)hypot_tb, METH_VARARGS,
     "Add docs here\n"},
    // NULL terminate Python looking at the object
     { NULL, NULL, 0, NULL }
};

PyMODINIT_FUNC init_toolbox(void) {
    Py_InitModule3("_toolbox", toolbox_methods,
                     "toolbox module");
}

在python中它是：

>>> import _toolbox
>>> _toolbox.hypot(*range(4, 10))
[4, 5, 6, 7, 8, 9]

解决方法:

我之前使用过这样的东西.这可能是一个糟糕的代码,因为我不是一个经验丰富的C编码器,但它对我有用.这个想法是,* args只是一个Python元组,你可以做任何你可以用Python元组做的事情.你可以查看http://docs.python.org/c-api/tuple.html.

int
ParseArguments(unsigned long arr[],Py_ssize_t size, PyObject *args) {
    /* Get arbitrary number of positive numbers from Py_Tuple */
    Py_ssize_t i;
    PyObject *temp_p, *temp_p2;


    for (i=0;i<size;i++) {
        temp_p = PyTuple_GetItem(args,i);
        if(temp_p == NULL) {return NULL;}

        /* Check if temp_p is numeric */
        if (PyNumber_Check(temp_p) != 1) {
            PyErr_SetString(PyExc_TypeError,"Non-numeric argument.");
            return NULL;
        }

        /* Convert number to python long and than C unsigned long */
        temp_p2 = PyNumber_Long(temp_p);
        arr[i] = PyLong_AsUnsignedLong(temp_p2);
        Py_DECREF(temp_p2);
        if (arr[i] == 0) {
            PyErr_SetString(PyExc_ValueError,"Zero doesn't allowed as argument.");
            return NULL;
        }
        if (PyErr_Occurred()) {return NULL; }
    }

    return 1;
}

我这样调用这个函数：

static PyObject *
function_name_was_here(PyObject *self, PyObject *args)
{
    Py_ssize_t TupleSize = PyTuple_Size(args);
    Py_ssize_t i;
    struct bigcouples *temp = malloc(sizeof(struct bigcouples));
    unsigned long current;

    if(!TupleSize) {
        if(!PyErr_Occurred()) 
            PyErr_SetString(PyExc_TypeError,"You must supply at least one argument.");
        free(temp);
        return NULL;
    }

    unsigned long *nums = malloc(TupleSize * sizeof(unsigned long));

    if(!ParseArguments(nums, TupleSize, args)){
        /* Make a cleanup and than return null*/
        return null;
    }

标签：c-3,python,python-c-extension
来源： https://codeday.me/bug/20190928/1829470.html