《扩展和嵌入Python解释器（译稿）》1.7 Extracting Parameters in Extension Functions

1.7 Extracting Parameters in Extension Functions

The PyArg_ParseTuple() function is declared as follows:

PyArg_ParseTuple()函数是以以下形式声明的

int PyArg_ParseTuple(PyObject *arg, char *format, …);

The argargument must be a tuple object containing an argument list passed from Python to a C function. The formatargument must be a format string, whose syntax is explained in “Parsing arguments and building values” in the Python/C API Reference Manual. The remaining arguments must be addresses of variables whose type is determined by the format string.

arg参数必须是一个由Python传入C函数的存储了参数列表的元组对象。format参数必须为一个格式字符串，格式字符的语法在Python/C API Reference Manual中的Parsing arguments and building values说明了。余下的参数必须为变量的地址，变量的类型由格式字符串决定。

Note that while PyArg_ParseTuple() checks that the Python arguments have the required types, it cannot check the validity of the addresses of C variables passed to the call: if you make mistakes there, your code will     probably crash or at least overwrite random bits in memory. So be careful!

注意，虽然可以检测Python的参数类型是否符合要求，但却不能检测传入到调用者的C变量的地址的可用性：如果你在那里犯错了，你的代码可能发生冲突，至少也会导致随机覆盖重写内存中的位。因而要小心！

Note that any Python object references which are provided to the caller are borrowed references;do not decrement their reference count!

注意，任何提供给调用者的Python对象的引用都是借引用，所以不要减少它们的引用计数。

Some example calls:

一些调用的例子：

int ok;

int i, j;

long k, l;

const char *s;

int size;

ok = PyArg_ParseTuple(args, ""); /* No arguments */

/* Python call: f() */

ok = PyArg_ParseTuple(args, "s", &s); /* A string */

/* Possible Python call: f(’whoops!’) */

ok = PyArg_ParseTuple(args, "lls", &k, &l, &s); /* Two longs and a string */

/* Possible Python call: f(1, 2, ’three’) */

ok = PyArg_ParseTuple(args, "(ii)s#", &i, &j, &s, &size);

/* A pair of ints and a string, whose size is also returned */

/* Possible Python call: f((1, 2), ’three’) */

{

const char *file;

const char *mode = "r";

int bufsize = 0;

ok = PyArg_ParseTuple(args, "s|si", &file, &mode, &bufsize);

/* A string, and optionally another string and an integer */

/* Possible Python calls:

f(’spam’)

f(’spam’, ’w’)

f(’spam’, ’wb’, 100000) */

}

{

int left, top, right, bottom, h, v;

ok = PyArg_ParseTuple(args, "((ii)(ii))(ii)",

&left, &top, &right, &bottom, &h, &v);

/* A rectangle and a point */

/* Possible Python call:

f(((0, 0), (400, 300)), (10, 10)) */

}

{

Py_complex c;

ok = PyArg_ParseTuple(args, "D:myfunction", &c);

/* a complex, also providing a function name for errors */

/* Possible Python call: myfunction(1+2j) */

}