来自python字符串的C char数组

Question

我在 python 中有一个字符串列表，我试图将其传递给 C 扩展以进行字符分析。到目前为止，我已经将列表分解为它们各自的字符串 PyObjects。接下来，我希望将这些字符串拆分为单独的字符，这样每个字符串 PyObject 现在都是一个对应的 C 类型字符数组。不过，我似乎无法弄清楚如何做到这一点。

这是我到目前为止所拥有的：目前在构建 .pyd 文件后，它将返回一个 1 的列表作为 Python 的填充符（因此其他一切都有效），我只是不知道如何将字符串 PyObject 拆分为C型字符数组。

--- cExt.c ---

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

static int *CitemCheck(PyObject *commandString, int commandStringLength) {

    // HAALP

    //char* commandChars = (char*) malloc(commandStringLength*sizeof(char*));

    // char c[] = PyString_AsString("c", commandString);
    // printf("%c" , c);
    // printf("%s", PyString_AsString(commandString));
    // for (int i=0; i<sizeof(commandChars)/sizeof(*commandChars); i++) {
    //     printf("%s", PyString_AsString(commandString));
    //     printf("%c", commandChars[i]);
    // }
    return 1; // TODO: RETURN PROPER RESULTANT
}

static PyObject *ClistCheck(PyObject *commandList, int commandListLength) {

    PyObject *results = PyList_New(commandListLength);

    for (int index = 0; index < commandListLength; index++) {
        PyObject *commandString;
        commandString = PyList_GetItem(commandList, index);
        int commandStringLength = PyObject_Length(commandString);

        // CitemCheck should take string PyObject and its length as int
        int x = CitemCheck(commandString, commandStringLength);

        PyObject* pyItem = Py_BuildValue("i", x);
        PyList_SetItem(results, index, pyItem);
    }
    return results;
}

static PyObject *parseListCheck(PyObject *self, PyObject *args) {
    PyObject *commandList;
    int commandListLength;

    if (!PyArg_ParseTuple(args, "O", &commandList)){
        return NULL;
    }

    commandListLength = PyObject_Length(commandList);

    return Py_BuildValue("O", ClistCheck(commandList, commandListLength));
}

static char listCheckDocs[] = 
    ""; // TODO: ADD DOCSTRING

static PyMethodDef listCheck[] = {
 {"listCheck", (PyCFunction) parseListCheck, METH_VARARGS, listCheckDocs},
 {NULL,NULL,0,NULL}
};

static struct PyModuleDef DCE = {
    PyModuleDef_HEAD_INIT,
    "listCheck",
    NULL,
    -1,
    listCheck
};

PyMODINIT_FUNC PyInit_cExt(void){
    return PyModule_Create(&DCE);
}

作为参考，我的临时扩展构建文件：

--- _c_setup.py --- 
(located in same folder as cExt.c)
"""
to build C files, pass:

python _c_setup.py build_ext --inplace clean --all

in command prompt which is cd'd to the file's dierctory
"""
import glob
from setuptools import setup, Extension, find_packages
from os import path

here = path.abspath(path.dirname(__file__))
files = [path.split(x)[1] for x in glob.glob(path.join(here, '**.c'))]

extensions = [Extension(
    path.splitext(x)[0], [x]
) for x in files]

setup(
    ext_modules = extensions,
)

Answer 1

您可以使用 PyUnicode_AsEncodedString，其中

编码一个 Unicode 对象并将结果作为 Python 字节对象返回。 encoding 和 errors 与 Unicode encode() 方法中的同名参数含义相同。使用 Python 编解码器注册表查找要使用的编解码器。如果编解码器引发异常，则返回 NULL。

见https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_AsEncodedString

然后使用 PyBytes_AsString 你会得到一个指向带有终止 NUL 字节的内部缓冲区的指针。这个缓冲区既不能被释放也不能被修改。如果您需要副本，可以使用例如strdup。

见https://docs.python.org/3/c-api/bytes.html#c.PyBytes_AsString

稍微修改一下你的代码，它可能看起来像这样：

PyObject *encodedString = PyUnicode_AsEncodedString(commandString, "UTF-8", "strict");
if (encodedString) { //returns NULL if an exception was raised
    char *commandChars = PyBytes_AsString(encodedString); //pointer refers to the internal buffer of encodedString
    if(commandChars) {
        printf("the string '%s' consists of the following chars:\n", commandChars);
        for (int i = 0; commandChars[i] != '\0'; i++) {
            printf("%c ", commandChars[i]);
        }
        printf("\n");
    }
    Py_DECREF(encodedString);
}

如果有人会测试：

import cExt

fruits = ["apple", "pears", "cherry", "pear", "blueberry", "strawberry"]         
res = cExt.listCheck(fruits)
print(res)

输出将是：

the string 'apple' consists of the following chars:
a p p l e 
the string 'pears' consists of the following chars:
p e a r s 
the string 'cherry' consists of the following chars:
c h e r r y 
the string 'pear' consists of the following chars:
p e a r 
the string 'blueberry' consists of the following chars:
b l u e b e r r y 
the string 'strawberry' consists of the following chars:
s t r a w b e r r y 
[1, 1, 1, 1, 1, 1]

与问题没有直接关系的旁注： 您的 CitemCheck 函数返回一个指向 int 的指针，但如果查看它的调用方式，您似乎想要返回一个 int 值。函数签名应该看起来更像这样：

static int CitemCheck(PyObject *commandString, int commandStringLength)

（注意 int 后删除的*）。