使用Python / C API将Python列表传递给C函数

Question

我最近开始使用Python / C API使用C代码为Python构建模块。我一直在尝试将Python的数字列表传递给C函数，但没有成功：

asdf_module.c

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <Python.h>

int _asdf(int low, int high, double *pr)
    // ...

    for (i = 0; i < range; i++)
    {
        printf("pr[%d] = %f\n", i, pr[i]);
    }

    // ...

    return 0;
}

static PyObject*
asdf(PyObject* self, PyObject* args)
{
    int low, high;
    double *pr;
    // maybe something about PyObject *pr ?

    if (!PyArg_ParseTuple(args, "iiO", &low, &high, &pr))
        return NULL;

    // how to pass list pr to _asdf?

    return Py_BuildValue("i", _asdf(low, high, pr));
}

static PyMethodDef AsdfMethods[] =
{
     {"asdf", asdf, METH_VARARGS, "..."},
     {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC
initasdf(void)
{
    (void) Py_InitModule("asdf", AsdfMethods);
}

使用setup.py构建模块：

from distutils.core import setup, Extension

module1 = Extension('asdf', sources = ['asdf_module.c'])

setup (name = 'asdf',
        version = '1.0',
        description = 'This is a demo package',
        ext_modules = [module1])

使用test_module.py中的模块：

import asdf

print asdf.asdf(-2, 3, [0.7, 0.0, 0.1, 0.0, 0.0, 0.2])

但是，我得到的输出是：

pr [0] = 0.000000

pr [1] = 0.000000

pr [2] = 0.000000

pr [3] = 0.000000

pr [4] = 0.000000

pr [5] = -nan

另外，代替_asdf返回0，它如何返回n值数组（n固定数字在哪里）？

Answer 1

本示例将向您展示如何

1. 获取列表的长度
2. 分配存储以用于 double
3. 获取列表中的每个元素
4. 将每个元素转换为 double
5. 将每个转换后的元素存储在数组中

这是代码：

#include "Python.h"

int _asdf(double pr[], int length) {
    for (int index = 0; index < length; index++)
        printf("pr[%d] = %f\n", index, pr[index]);
    return 0;
}

static PyObject *asdf(PyObject *self, PyObject *args)
{
    PyObject *float_list;
    int pr_length;
    double *pr;

    if (!PyArg_ParseTuple(args, "O", &float_list))
        return NULL;
    pr_length = PyObject_Length(float_list);
    if (pr_length < 0)
        return NULL;
    pr = (double *) malloc(sizeof(double *) * pr_length);
    if (pr == NULL)
        return NULL;
    for (int index = 0; index < pr_length; index++) {
        PyObject *item;
        item = PyList_GetItem(float_list, index);
        if (!PyFloat_Check(item))
            pr[index] = 0.0;
        pr[index] = PyFloat_AsDouble(item);
    }
    return Py_BuildValue("i", _asdf(pr, pr_length));
}

注意：删除空格和大括号以防止滚动代码。

测试程序

import asdf
print asdf.asdf([0.7, 0.0, 0.1, 0.0, 0.0, 0.2])

输出量

pr[0] = 0.700000
pr[1] = 0.000000
pr[2] = 0.100000
pr[3] = 0.000000
pr[4] = 0.000000
pr[5] = 0.200000
0