C++中嵌入python程序——参数传递

C++中嵌入python程序——参数传递

前面两篇博客已经介绍如何在C++中嵌套使用 python，但是在实际使用中，我们需要向python传递各种各样的参数，这样的程序才具有更高的灵活性。下面简单介绍一下参数传递，整体代码不再给出，只介绍几个核心语法，只要掌握就能与前面代码结合起来生成完整可用的代码。

PyObject_CallMethod(pClass, “class_method”, “O”, pInstance)
参数分别为 PyObject（类），string（类方法），string（O表示参数为PyObject） ，PyObject（类实例）

PyObject_CallFunction(pFun, “O”, pyores)
参数分别为 PyObject（函数），string（O表示参数为PyObject） ，PyObject（函数中使用的参数）

问题来了，函数有多个参数怎么办，参数怎么传递？别担心，有多少个我们就写多少个：
PyObject_CallFunction(pFun, “OO…O”, PyObject 1,PyObject 2…PyObject n)
中间的O可替换成参数类型说明符中的任意一个，比如字符串s，int型变量i等等

创建一个元组
PyObject *pArgs = PyTuple_New(3);
PyTuple_SetItem(pArgs, 0, Py_BuildValue(“i”, 1));//0—序号 i表示创建int型变量
PyTuple_SetItem(pArgs, 1, Py_BuildValue(“i”, 2));
PyTuple_SetItem(pArgs, 2, Py_BuildValue(“i”, 3));

PyEval_CallObject(pFunc, pArgs); //调用函数，pArgs元素个数与被调函数参数个数一致

PyObject *pDict = PyDict_New(); //创建字典类型变量
PyDict_SetItemString(pDict, “Name”, Py_BuildValue(“s”, “Zhangsan”)); //往字典类型变量中填充数据
PyDict_SetItemString(pDict, “Address”, Py_BuildValue(“s”, “BeiJing”));

将上述字典赋值给元组
PyObject *pArgs = PyTuple_New(1);
PyTuple_SetItem(pArgs, 0, pDict)

python返回给C++的是PyObject类型，如果我想在纯C++程序里使用它怎么办：（可以使用下面这个函数
char * PyString_AsString（PyObject*）

至此，利用上面的几个基本参数传递方法，已经可以创建灵活性较强的C++/python程序。

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传入参数类型说明符

百度一下发现相关的内容一大堆，从这里http://www.cnblogs.com/lancelod/p/4036922.html摘抄了下来
s (string) [char *]
Convert a null-terminated C string to a Python object. If the C string pointer is NULL, None is used.
s# (string) [char *, int]
Convert a C string and its length to a Python object. If the C string pointer is NULL, the length is ignored and None is returned.
z (string or None) [char *]
Same as s.
z# (string or None) [char *, int]
Same as s#.
u (Unicode string) [Py_UNICODE *]
Convert a null-terminated buffer of Unicode (UCS-2 or UCS-4) data to a Python Unicode object. If the Unicode buffer pointer is NULL, Noneis returned.
u# (Unicode string) [Py_UNICODE *, int]
Convert a Unicode (UCS-2 or UCS-4) data buffer and its length to a Python Unicode object. If the Unicode buffer pointer is NULL, the length is ignored and None is returned.
i (integer) [int]
Convert a plain C int to a Python integer object.
b (integer) [char]
Convert a plain C char to a Python integer object.
h (integer) [short int]
Convert a plain C short int to a Python integer object.
l (integer) [long int]
Convert a C long int to a Python integer object.
B (integer) [unsigned char]
Convert a C unsigned char to a Python integer object.
H (integer) [unsigned short int]
Convert a C unsigned short int to a Python integer object.
I (integer/long) [unsigned int]
Convert a C unsigned int to a Python integer object or a Python long integer object, if it is larger than sys.maxint.
k (integer/long) [unsigned long]
Convert a C unsigned long to a Python integer object or a Python long integer object, if it is larger than sys.maxint.
L (long) [PY_LONG_LONG]
Convert a C long long to a Python long integer object. Only available on platforms that support long long.
K (long) [unsigned PY_LONG_LONG]
Convert a C unsigned long long to a Python long integer object. Only available on platforms that support unsigned long long.
n (int) [Py_ssize_t]
Convert a C Py_ssize_t to a Python integer or long integer.

New in version 2.5.

c (string of length 1) [char]
Convert a C int representing a character to a Python string of length 1.
d (float) [double]
Convert a C double to a Python floating point number.
f (float) [float]
Same as d.
D (complex) [Py_complex *]
Convert a C Py_complex structure to a Python complex number.
O (object) [PyObject *]
Pass a Python object untouched (except for its reference count, which is incremented by one). If the object passed in is a NULL pointer, it is assumed that this was caused because the call producing the argument found an error and set an exception. Therefore, Py_BuildValue()will return NULL but won’t raise an exception. If no exception has been raised yet, SystemError is set.
S (object) [PyObject *]
Same as O.
N (object) [PyObject *]
Same as O, except it doesn’t increment the reference count on the object. Useful when the object is created by a call to an object constructor in the argument list.
O& (object) [converter, anything]
Convert anything to a Python object through a converter function. The function is called with anything (which should be compatible withvoid *) as its argument and should return a “new” Python object, or NULL if an error occurred.
(items) (tuple) [matching-items]
Convert a sequence of C values to a Python tuple with the same number of items.
[items] (list) [matching-items]
Convert a sequence of C values to a Python list with the same number of items.
{items} (dictionary) [matching-items]
Convert a sequence of C values to a Python dictionary. Each pair of consecutive C values adds one item to the dictionary, serving as key and value, respectively.