Four Ways of Mixing python with C and C + + Summary of of

Mixed compilation has two meanings,

One is to write C in python

One is python written in C

This paper is mainly simplified and convenient to use.

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First, Python calls C dynamic link library (using ctypes)

pycall.c

/***gcc -o libpycall.so -shared -fPIC pycall.c*/ 
#include <stdio.h> 
#include <stdlib.h> 
int foo(int a, int b) 
{ 
 printf("you input %d and %d\n", a, b); 
 return a+b; 
}

pycall.py

import ctypes 
ll = ctypes.cdll.LoadLibrary  
lib = ll("./libpycall.so")  
lib.foo(1, 3) 
print '***finish***' 

Operation method:

gcc -o libpycall.so -shared -fPIC pycall.c
python pycall.py

Second, Python calls C + + (class) dynamic link library (using ctypes)

pycallclass.cpp

#include <iostream> 
using namespace std; 
 
class TestLib 
{ 
  public: 
    void display(); 
    void display(int a); 
}; 
void TestLib::display() { 
  cout<<"First display"<<endl; 
} 
 
void TestLib::display(int a) { 
  cout<<"Second display:"<<a<<endl; 
} 
extern "C" { 
  TestLib obj; 
  void display() { 
    obj.display();  
   } 
  void display_int() { 
    obj.display(2);  
   } 
}

pycallclass.py

import ctypes 
so = ctypes.cdll.LoadLibrary  
lib = so("./libpycallclass.so")  
print 'display()' 
lib.display() 
print 'display(100)' 
lib.display_int(100)

Operation method:

g++ -o libpycallclass.so -shared -fPIC pycallclass.cpp
python pycallclass.py

Third, Python calls C and C + + executable programs

main.cpp

#include <iostream> 
using namespace std; 
int test() 
{ 
  int a = 10, b = 5; 
  return a+b; 
} 
int main() 
{ 
  cout<<"---begin---"<<endl; 
  int num = test(); 
  cout<<"num="<<num<<endl; 
  cout<<"---end---"<<endl; 
}

main.py

import commands 
import os 
main = "./testmain" 
if os.path.exists(main): 
  rc, out = commands.getstatusoutput(main) 
  print 'rc = %d, \nout = %s' % (rc, out) 
 
print '*'*10 
f = os.popen(main)  
data = f.readlines()  
f.close()  
print data 
 
print '*'*10 
os.system(main)

Run the method (only this one is not generated. so and then called by the python file):

g++ -o testmain main.cpp
python main.py

Fourth, extend Python (C + + writes extension module for Python) (super troublesome one)

Extest2.c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
 
int fac(int n) 
{ 
  if (n < 2) return(1); 
  return (n)*fac(n-1); 
} 
 
char *reverse(char *s) 
{ 
  register char t, 
      *p = s, 
      *q = (s + (strlen(s) - 1)); 
 
  while (s && (p < q)) 
  { 
    t = *p; 
    *p++ = *q; 
    *q-- = t; 
  } 
  return(s); 
} 
 
int test() 
{ 
  char s[BUFSIZ]; 
  printf("4! == %d\n", fac(4)); 
  printf("8! == %d\n", fac(8)); 
  printf("12! == %d\n", fac(12)); 
  strcpy(s, "abcdef"); 
  printf("reversing 'abcdef', we get '%s'\n", \ 
    reverse(s)); 
  strcpy(s, "madam"); 
  printf("reversing 'madam', we get '%s'\n", \ 
    reverse(s)); 
  return 0; 
} 
 
#include "Python.h" 
 
static PyObject * 
Extest_fac(PyObject *self, PyObject *args) 
{ 
  int num; 
  if (!PyArg_ParseTuple(args, "i", &num)) 
    return NULL; 
  return (PyObject*)Py_BuildValue("i", fac(num)); 
} 
 
static PyObject * 
Extest_doppel(PyObject *self, PyObject *args) 
{ 
  char *orig_str; 
  char *dupe_str; 
  PyObject* retval; 
 
  if (!PyArg_ParseTuple(args, "s", &orig_str)) 
    return NULL; 
  retval = (PyObject*)Py_BuildValue("ss", orig_str, 
    dupe_str=reverse(strdup(orig_str))); 
  free(dupe_str);       
  return retval; 
} 
 
static PyObject * 
Extest_test(PyObject *self, PyObject *args) 
{ 
  test(); 
  return (PyObject*)Py_BuildValue(""); 
} 
 
static PyMethodDef 
ExtestMethods[] = 
{ 
  { "fac", Extest_fac, METH_VARARGS }, 
  { "doppel", Extest_doppel, METH_VARARGS }, 
  { "test", Extest_test, METH_VARARGS }, 
  { NULL, NULL }, 
}; 
 
void initExtest() 
{ 
  Py_InitModule("Extest", ExtestMethods); 
}

setup.py

#!/usr/bin/env python 
 
from distutils.core import setup, Extension 
 
MOD = 'Extest' 
setup(name=MOD, ext_modules=[Extension(MOD, sources=['Extest2.c'])])

Operation method:

python setup.py build
cd build/lib.linux-x86_64-2.7

Enter python Interactive Mode > > >

import Extest
Extest.test()