An example for http://stackoverflow.com/questions/34445045/passing-python-functions-to-swig-wrapped-c-code

README.md

Instructions for Linux

Requires SWIG, CMake version 3.8 and above (the SWIG module has changed in 3.8, so previous verions will require a few minor modiciations)

1. Create a build directory and make it the current dir

mkdir build
cd build

2. Configure

cmake ..

3. Build

cmake --build .

4. Test

ctest

CMakeLists.txt

cmake_minimum_required(VERSION 3.8)

project(dummy)

find_package(PythonLibs 3 REQUIRED)
find_package(PythonInterp ${PYTHONLIBS_VERSION_STRING} REQUIRED)

find_package(SWIG REQUIRED)
include(${SWIG_USE_FILE})

if(PYTHONLIBS_VERSION_STRING MATCHES "^2.*$" )
    set(CMAKE_SWIG_FLAGS -classic)
else()
    set(CMAKE_SWIG_FLAGS -py3)
endif()

message("PYTHONLIBS_VERSION_STRING: ${PYTHONLIBS_VERSION_STRING}")
message("CMAKE_SWIG_FLAGS: ${CMAKE_SWIG_FLAGS}")

include_directories(example ${PYTHON_INCLUDE_PATH} ${CMAKE_CURRENT_SOURCE_DIR})

set_source_files_properties(example.i PROPERTIES CPLUSPLUS ON)

swig_add_library(example TYPE SHARED LANGUAGE python SOURCES example.i)
swig_link_libraries(example ${PYTHON_LIBRARIES})

enable_testing()
add_test(test1 ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/test_example_wrapper.py)

example.i

%module example

// a typemap for the callback, it expects the argument to be an integer
// whose value is the address of an appropriate callback function
%typemap(in) void (*f)(int, const char*) {
    $1 = (void (*)(int i, const char*))PyLong_AsVoidPtr($input);;
}

%{
    void use_callback(void (*f)(int i, const char* str));
%}

%inline
%{

// a C function that accepts a callback
void use_callback(void (*f)(int i, const char* str))
{
    f(100, "callback arg");
}

%}

%pythoncode
%{

import ctypes

# a ctypes callback prototype
py_callback_type = ctypes.CFUNCTYPE(None, ctypes.c_int, ctypes.c_char_p)

def use_callback(py_callback):

    # wrap the python callback with a ctypes function pointer
    f = py_callback_type(py_callback)

    # get the function pointer of the ctypes wrapper by casting it to void* and taking its value
    f_ptr = ctypes.cast(f, ctypes.c_void_p).value

    _example.use_callback(f_ptr)

%}

test_example.py

import example

# python callback
def py_callback(i, s):
    print('py_callback(%d, %s)'%(i, s))

example.use_callback(py_callback)

test_example_wrapper.py

# add the location of the compiled module is in the module search path

import sys
sys.path.append('.')

# run the actual example

import test_example