How to use c++ code in python

Everyone knows that the advantages of Python are high development efficiency and ease of use, while C has high operating efficiency. The two can complement each other, whether it is embedding C code in a Python project, or using Python to implement peripherals in a C project Functions, you may encounter the need for Python to call C modules.

#The following is a list of methods for exporting centralized C code into a Python interface. Let's learn together.

Original Export (Recommended learning: Python video tutorial)

The Python interpreter is implemented in C, so As long as our C data structure can be understood by Python, it can theoretically be called directly. We implement test1.cpp as follows

#include <Python.h>
int Add(int x, int y)
{
return x + y;
}
int Del(int x, int y)
{
return x - y;
}
PyObject* WrappAdd(PyObject* self, PyObject* args)
{
int x, y;
if (!PyArg_ParseTuple(args, "ii", &x, &y))
{
return NULL;
}
return Py_BuildValue("i", Add(x, y));
}
PyObject* WrappDel(PyObject* self, PyObject* args)
{
int x, y;
if (!PyArg_ParseTuple(args, "ii", &x, &y))
{
return NULL;
}
return Py_BuildValue("i", Del(x, y));
}
static PyMethodDef test_methods[] = {
{"Add", WrappAdd, METH_VARARGS, "something"},
{"Del", WrappDel, METH_VARARGS, "something"},
{NULL, NULL}
};
extern "C"
void inittest1()
{
Py_InitModule("test1", test_methods);   
}

The compilation command is as follows

g++ -fPIC -shared test1.cpp -I/usr/include/python2.7 -o test1.so

-fPIC: Generate position-independent target code, suitable for dynamic connection;
- L path: means searching for library files in the path directory, such as -L. means searching in the current directory;
-I path: means searching for header files in the path directory;
-o file: specifies the output file as file;
-shared: Generate a shared library file;

Run the Python interpreter and test as follows

>>> import test1
>>> test1.Add(1,2)
3

There are a few points to note here

If the name of the generated dynamic library is test1, the source file must have the inittest1 function, and the first parameter of Py_InitModule must be "test1", otherwise the Python import module will fail

If it is a cpp source file, the inittest1 function must be modified with extern "C". If it is a c source file, it is not required. The reason is that the Python interpreter will look for functions such as initxxx when importing libraries, and C and C encode function symbols differently. C will consider the function length and parameter type when encoding function symbols. Specifically, you can pass nm test1. So check the function symbols, and the c filt tool can decode the function prototype through the symbols.

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