Search


    Learn to Create Libraries for Python with C/C++

    Simple and functional!

    Learn to Create Libraries for Python with C/C++

    In this article we will see: how to create libraries for Python with C++, the process is similar to the post/video we saw on C++ for Lua.

    The libraries of several programming languages are written in C and C++, as the performance is much higher than writing in the language itself.

    There are a large number of libraries for Python that are written in C++, the most famous are:

    Creating a basic Hello World

    Let’s create a directory (libpycpp/) and a main.cpp file:

    mkdirlibpycpp
cd libpycpp
vim main.cpp

    01. Most basic code of all: Prints: Hello World

    main.cpp

    // 01. Include Python.h header
#include <Python.h>

// 02. Register the signature of your function
// and the logical content of your function
int world(){
   printf("Hello, World!\n");
   return 0;
}

// 03. Handles your function arguments
// and return to Python
static PyObject* world(PyObject* self, PyObject* args){
   return Py_BuildValue("s", world());
}

// 04. Creates an array of static type PyMethodDef
// which stores all your functions
static PyMethodDef hello_methods[] = {
   {"world", world, METH_VARARGS, "Print Hello World."},
   {NULL, NULL, 0, NULL} // Enter the end of the list
   // Python function | your role | arguments(METH_VARARGS = 1) | What does she do
};

// 05. Creates the structure with the name of the module you
// want to use in Python
static struct PyModuleDef hello_module = {
   PyModuleDef_HEAD_INIT, // Informs the base
   "hello", // The name of your library
   NULL, // The name of the documentation
   -1, // The module size, -1 is the maximum size
   hello_methods // The module name with underscore and methods at the end
};

// 06. Similar to the main() function, gateway to Python.
// The return type must be: PyMODINIT_FUNC
// The name must be PyInit_ the name of your lib (void arguments)
PyMODINIT_FUNC PyInit_hello(void){
   return PyModule_Create(&hello_module); // Return PyModule_Create and pointer & the PyModuleDef struct
}

    To compile:

    g++ -shared -o hello.so -fpic main.cpp -I /usr/include/python3.12 # Enter the version on your system

    Using:

    vim script.py

    import hello

hello.world()

    02. Using parameters for function

    1. Create a new base function:

    int add(int x, int y){
   return x + y;
}

    2. Create the return

    // Does not necessarily have to be the same name
static PyObject* add(PyObject* self, PyObject* args){
   int a, b;
   // ii = 2 integers
   if(!PyArg_ParseTuple(args, "ii", &a, &b)){
     return NULL;
   }
   // i = returns an integer
   return Py_BuildValue("i", add(a, b));
}

    3. Add to array

    static PyMethodDef hello_methods[] = {
   {"world", world, METH_VARARGS, "Print Hello World."},
   {"add", add, METH_VARARGS, "Add two number."}, // Add to list
   {NULL, NULL, 0, NULL} // Enter the end of the list
};

    Using:

    vim script.py

    import hello

print(hello.add(3, 6))

numb1 = 36
numb2 = 90

print("The sum is: ", hello.add(numb1, numb2))

    python script.py

    03. Creating a function that receives string

    1. Let’s call this function echo:
    int echo(const char* str){
   printf("%s", str);
   return 0;
}
    1. PyObject function:
    static PyObject* echo(PyObject* self, PyObject* args){
   const char* str;
   if(!PyArg_ParseTuple(args, "s", &str)){
     return NULL;
   }
   return Py_BuildValue("s", echo(str));
}
    1. Add to the array:
    static PyMethodDef hello_methods[] = {
   {"world", world, METH_VARARGS, "Print Hello World."},
   {"add", add, METH_VARARGS, "Add two number."},
   {"echo", echo, METH_VARARGS, "Print string"}, // HERE
   {NULL, NULL, 0, NULL} // Enter the end of the list
};

    Compile and test:

    hello.echo("Thanks, this is cool!\n")

    I made the library of that code from video that plays MP3 with C++ and created a lib.

    If you want to test on your machine, follow the steps:

    i1. Copy and create the files (playmp3.hpp and playmp3.cpp) from the playmp3 video post available at: 🎶 How to Play MP3 with C++ 🎻 🎼 Code Music

    1. Create main.cpp and add the code below:
    #include <Python.h>
#include "playmp3.hpp"

int mp3(char* song){
  auto p = std::make_unique<PlayMP3>();
  p->music(song);
  p->play();
  return 0;
}

static PyObject* mp3(PyObject* self, PyObject* args){
  char* music;
  if (!PyArg_ParseTuple(args, "s", &music)) {
    return NULL;
  }
  mp3(music);
  return Py_BuildValue("");
}

static PyMethodDef playmp3_methods[] = {
  {"mp3", mp3, METH_VARARGS, "Play MP3"},
  {NULL, NULL, 0, NULL}
};

static struct PyModuleDef playmp3_module = {
  PyModuleDef_HEAD_INIT,
  "playmp3",
  NULL,
  -1,
  playmp3_methods
};

PyMODINIT_FUNC PyInit_playmp3(void) {
  return PyModule_Create(&playmp3_module);
}
    1. Add the libalsa.so path to the environment variable: LD_LIBRARY_PATH:
    echo export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$(dirname "$(find /usr/lib* -name "libalsa.so" 2>/dev/null)") >> ~/.bashrc
    1. Close and open the terminal or run the command below:
    source ~/.bashrc
    1. Compile:
    g++ -shared -o playmp3.so -fpic main.cpp playmp3.cpp \
   -I /usr/include/python* \# Change to the path on your system
   -lmpg123 -lao $(find /usr/lib* -name "libalsa.so")
    1. Create a Python file: player.py
    import playmp3 as play
play.mp3("music.mp3")

    In music.mp3 replace with the song you want to listen to!

    Then just run:

    python player.py

    If you want to use the library directly on your system:

    sudo mv playmp3.so /usr/local/lib
echo 'export PYTHONPATH="${PYTHONPATH}:/usr/local/lib"' >> ~/.bashrc
source ~/.bashrc

    If you want to use a different output plugin for libao, such as the “oss” (Open Sound System) plugin, use:

    export AO_DRIVER=oss
python player.py

    Watch the video

    The video is in Portuguese, but it is possible to follow it even without audio.

    For more information, visit: https://docs.python.org/3/c-api/index.html

    python cpp clanguage

    Share

    Comments