《扩展和嵌入Python解释器（译稿）》1.8 Keyword Parameters for Extension Functions

1.8 Keyword Parameters for Extension Functions 扩展模块的关键字参数

The PyArg_ParseTupleAndKeywords()function is declared as follows:

PyArg_ParseTupleAndKeywords()函数是以以下的形式声明的：

int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict, char *format, char *kwlist[], …);

The argand formatparameters are identical to those of the PyArg_ParseTuple()function. The kwdict parameter is the dictionary of keywords received as the third parameter from the Python runtime. The kwlistparameter is a NULL-terminated list of strings which identify the parameters; the names are matched with the typeinformation from formatfrom left to right. On success, PyArg_ParseTupleAndKeywords()returns true, otherwise it returns false and raises an appropriate exception.

arg和format参数与PyArg_ParseTuple()函数中是同样的。kwdict参数是一个关键字的字典，是从Python运行环境中接收到的第三个参数。kwdict参数是一个以NULL表示终止的字符串列表，列表中的字符串标识的是关键字参数；关键字的名字自左向右地与从format接收到的类型信息相匹配。匹配成功时PyArg_ParseT- upleAndKeywords()返回true，否则将返回false并抛出适当的异常。

Note:Nested tuples cannot be parsed when using keyword arguments! Keyword parameters passed in which are not present in the kwlistwill cause TypeErrorto be raised.

注意：使用关键字参数时，嵌套元组无法被解析！传入未出现于kwlist的关键字参数，会引发TypeError抛出。

Here is an example module which uses keywords, based on an example by Geoff Philbrick (philbrick@hks.com):

这有一个使用了关键字参数的例子，是基于Geoff Philbrick (philbrick@hks.com)的一个例子:

#include "Python.h"

static PyObject *

keywdarg_parrot(PyObject *self, PyObject *args, PyObject *keywds)

{

    int voltage;

    char *state = "a stiff";

    char *action = "voom";

    char *type = "Norwegian Blue";

    static char *kwlist[] = {"voltage", "state", "action", "type", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|sss", kwlist, &voltage, &state, &action, &type))

        return NULL;

    printf("– This parrot wouldn’t %s if you put %i Volts through it.\n", action, voltage);

    printf("– Lovely plumage, the %s — It’s %s!\n", type, state);

    Py_INCREF(Py_None);

    return Py_None;

}

static PyMethodDef keywdarg_methods[] = {

/* The cast of the function is necessary since PyCFunction values

* only take two PyObject* parameters, and keywdarg_parrot() takes

* three.

*/

{

    "parrot", (PyCFunction)keywdarg_parrot, METH_VARARGS | METH_KEYWORDS,

    "Print a lovely skit to standard output."},

    {NULL, NULL, 0, NULL} /* sentinel */

};

void

initkeywdarg(void)

{

/* Create the module and add the functions */

    Py_InitModule("keywdarg", keywdarg_methods);

}