Modern/2020 从 Python 调用 C++ 代码的方法

Question

I am trying to call a C++ function from a Python script. I have seen different solutions on Stackoverflow from 2010-2015 but they are all using complicated packages and was hoping for something easier/newer and more sophisticated. The C++ function I am trying to call takes in a double variable and returns a double.

double foo(double var1){
    double result = ...
    return result;
}

Answer 1

Python has ctypes package which allows calling functions in DLLs or shared libraries. Compile your C++ project into a shared library (.so) on Linux, or DLL on Windows. Export the functions you wish to expose outside.

C++ supports function overloading, to avoid ambiguity in the binary code, additional information is added to function names, known as name mangling . Whereas, in C function names are unchanged, to ensure no name is changed, simply place inside an extern “C” block.

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Demo: In this dummy demo, our library has a single function, taking an int and printing it.

lib.cpp

#include <iostream>

int Function(int num) 
{
    std::cout << "Num = " << num << std::endl;
    return 0;
}

extern "C" {
    int My_Function(int a)
    {
        return Function(a);
    }
}

We will compile this into a shared object first

g++ -fPIC -shared -o libTest.so lib.cpp

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Now we will utilized ctypes, to load the shared object/dll and functions.

myLib.py

import ctypes
import sys
import os 

dir_path = os.path.dirname(os.path.realpath(__file__))
handle = ctypes.CDLL(dir_path + "/libTest.so")     

handle.My_Function.argtypes = [ctypes.c_int] 
  
def My_Function(num):
    return handle.My_Function(num)    

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For our test, we will call the function with num = 16

test.py

from myLib import *

My_Function(16)

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The expected out as well.