How to call C / C++ from Python?

Last Updated : 29 Jul, 2020

In order to take advantage of the strength of both languages, developers use Python bindings which allows them to call C/C++ libraries from python.

Now, the question arises that why there is a need for doing this?

As we know that, C has faster execution speed and to overcome the limitation of Global Interpreter Lock(GIL) in python, python bindings are helpful.
We have a large, stable and tested library in C/C++, which will be advantageous to use.
For performing large scale testing of the systems using Python test tools.

Let’s see the C code which we want to execute with Python :

C++

#include <iostream> 
class Geek{ 
    public: 
        void myFunction(){ 
            std::cout << "Hello Geek!!!" << std::endl; 
        } 
}; 
int main() 
{ 
    // Creating an object 
    Geek t;  
  
    // Calling function 
    t.myFunction();   
   
    return 0; 
} 

We have to provide those cpp declarations as extern “C” because ctypes can only interact with C functions.

C++

extern "C" { 
    Geek* Geek_new(){ return new Geek(); } 
    void Geek_myFunction(Geek* geek){ geek -> myFunction(); } 
}

Now, compile this code to the shared library :

Finally, write the python wrapper:

Python3

# import the module 
from ctypes import cdll 
  
# load the library 
lib = cdll.LoadLibrary('./libgeek.so') 
  
# create a Geek class 
class Geek(object): 
  
    # constructor 
    def __init__(self): 
  
        # attribute 
        self.obj = lib.Geek_new() 
  
    # define method 
    def myFunction(self): 
        lib.Geek_myFunction(self.obj) 
  
# create a Geek class object 
f = Geek() 
  
# object method calling 
f.myFunction()

Output :

Hello Geek!!!

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