Python calls the C function

Python calls C

A typical Python extension should contain at least three parts: Export functions, method lists, and initialization functions. Example:

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example.cintfact(intn){        if(n <= 1)        return1;        else        returnn * fact(n - 1);}wrap.c#include <Python.h>PyObject* wrap_fact(PyObject* self, PyObject* args){        intn, result;                if(! PyArg_ParseTuple(args, "i:fact", &n))        return NULL;        result = fact(n);        returnPy_BuildValue("i", result);}staticPyMethodDef exampleMethods[] ={        {"fact", wrap_fact, METH_VARARGS, "Caculate N!"},        {NULL, NULL}};voidinitexample(){        PyObject* m;        m = Py_InitModule("example", exampleMethods);}

1. Export function to use a function in the C language in the Python interpreter, first write the appropriate export function for it, the export function in the above example is wrap_fact. In Python's C language extension, all the exported functions have the same function prototypes:

1	PyObject* method(PyObject* self, PyObject* args);

The function is an interface between the Python interpreter and the C function, with two parameters: Self and args. The parameter self is only used when the C function is implemented as an inline method (built-in), usually with a value of NULL (NULL). The parameter args contains all the parameters that the Python interpreter will pass to the C function, usually using the function pyarg_parsetuple () provided by the Python C extension interface to obtain these parameter values. All the exported functions return a pyobject pointer, and if the corresponding C function does not have a true return value (that is, the return value type is void), then a global None object (Py_none) should be returned, and its reference count will be increased by 1, as follows:

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PyObject* method(PyObject *self, PyObject *args){        Py_INCREF(Py_None);        returnPy_None;}

2. The method list method list shows all the methods that can be used by the Python interpreter, and the corresponding method list for the above example is:

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static   pymethoddef examplemethods[] = {          Code class= "Java plain" >{ "fact" , Wrap_fact, meth_ varargs,  "Caculate n!"          {null, NULL} };

Each item in the method list consists of four parts: The method name, the export function, the parameter passing method, and the method description. The method name is the name used when calling the method from the Python interpreter. The parameter passing method specifies the specific form of the python to pass the parameter to the C function, the optional two ways are Meth_varargs and meth_keywords, in which Meth_varargs is the standard form of the parameter passing, It passes the parameters between the Python interpreter and the C function through a python tuple, and if Meth_keyword is used, the Python interpreter and the C function will pass the argument between the two through the Python dictionary type.

3. Initialization function All Python extensions must have an initialization function so that the Python interpreter can initialize the module correctly. The Python interpreter specifies that all function names for the initialization function must begin with INIT and add the module's name. For module example, the corresponding initialization function is:

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voidinitexample(){        PyObject* m;        m = Py_InitModule("example", exampleMethods);}

When the Python interpreter needs to import the module, it will find the appropriate initialization function based on the name of the module and, once found, call the function to do the appropriate initialization, and initialize the function by calling the function Py_initmodule () provided by Python's C extension interface. To register all the available methods in the module with the Python interpreter.

4. Compiled under Linux, compiled into so library, Python can import directly. Under Windows, you need to modify the suffix of the DLL to Pyd,python to be recognized.

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gcc -fpic -c -I/usr/include/python2.5\-I /usr/lib/python2.5/config \example.c wrapper.cgcc -shared -o example.so example.o wrapper.o

5. Python calls

1234	>>> importexample>>> example.fact(4)24>>>

Python calls the C function