Import C++ function into Python program

Question

I'm experimenting with python functions right now. I've found a way to import python functions into c/c++ code, but not the other way around.

I have a c++ program written and it has a certain function in it. I'd like to "import" the compiled c++ program into my python script and call the c++ function.

For simplicity, say the c++ function is as simple as:

int square(x)
{
  return x*x;
}

and the compiled program is named Cprog.

I'd like my python script to be something like:

import Cprog

print Cprog.square(4)

Is this possible? I've searched the internet to no avail and I'm hoping one of you gurus might have a clever way of going about this...

Solution 1

Here is a little working completion of the simple example above. Although the thread is old, I think it is helpful to have a simple all-embracing guide for beginners, because I also had some problems before.

function.cpp content (extern "C" used so that ctypes module can handle the function):

extern "C" int square(int x)
{
  return x*x;
}

wrapper.py content:

import ctypes
print(ctypes.windll.library.square(4)) # windows
print(ctypes.CDLL('./library.so').square(4)) # linux or when mingw used on windows

Then compile the function.cpp file (by using mingw for example):

g++ -shared -c -fPIC function.cpp -o function.o

Then create the shared object library with the following command (note: not everywhere are blanks):

g++ -shared -Wl,-soname,library.so -o library.so function.o

Then run the wrapper.py an the program should work.

Solution 2

If you build your program as a shared library/DLL, you could use ctypes to call it.

import ctypes
print ctypes.windll.cprog.square(4) # windows
print ctypes.CDLL('cprog.so').square(4) # linux

Solution 3

You need to create a python module with that function in it. There are three main ways:

1. Using Swig - this reads your c code and creates a python module from it.
2. Hand coded using the python c api.
3. Using Boost::Python (often the easiest way).

This pdf covers 1 and 2. This page will tell you how to use Boost::Python.

You cannot (easily) use a function that is in a c/c++ program - it must be in a static library (which you can also link your c/c++ program against).

EDIT - Cython Is also worth a mention.

Solution 4

You want to extend python with a C/C++ module. The following Python documentation is a good place to start reading: http://docs.python.org/extending/extending.html

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