Python C Extension implementation on Kivy Android

This section will give an basic implementation of python C extension on kivy android using recipe for buildozer / p4a

Template for building the Android application

https://github.com/VICTORVICKIE/Kivy_Python_C_Extension_Demo

Kivy app

Create a project folder (Kivy_Python_C_Extension_Demo)

Directory Structure for Project

 Kivy_Python_C_Extension_Demo
 |
 ├── custom_lib
 |
 ├── python-for-android
 |
 └── main.py
 |
 └── buildozer.spec

Create a basic kivy app (main.py)

main.py

from kivy.app import App
from kivy.uix.label import Label

from custom_lib import custom_module

class PyCExtensionApp(App):

def build(self):
    return Label(text=custom_module.custom_hello())


if __name__ == '__main__':
    PyCExtensionApp().run()

This app just displays the text of string from the C Extension for demonstration.

C Extension

In the project directory

create a folder for the library (custom_lib) this contains all the requirements for the C Extension

setup.py / setup.cfg

and src folder format package (custom_lib, This is different from previous one!)

In the src folder we need a __init__.py for package and a module file (Here C Extension)

And the structure should look similar to this

Directory Structure for Library

 custom_lib
 |
 ├── setup.cfg
 |
 ├── setup.py
 |
 └── custom_lib
     |
     ├── custom_module.c
     |
     └── __init__.py

In custom_module.c

custom_module.c

#include <Python.h>

static PyObject* custom_hello(PyObject* self){
    return PyUnicode_FromString("Hello from Custom Lib");
}

static struct PyModuleDef methods[] = {

    {"custom_hello", (PyCFunction)custom_hello, METH_NOARGS},
    {NULL, NULL}
};

static struct PyModuleDef module = {
    PyModuleDef_HEAD_INIT,
    "custom_module",
    NULL,
    -1,
    methods
};

PyMODINIT_FUNC PyInit_custom_module(void) {
    return PyModule_Create(&module);
}

Setuptools

setup.py

from setuptools import find_packages, Extension, setup

setup(

    name = 'custom_lib',

    version = '0.1',

    description = 'This package contains some sample hello world C code',

    author = 'VIGNESH KUMAR S',

    author_email = 's.vickie14@gmail.com',

    url = 'https://github.com/VICTORVICKIE/Kivy_Python_C_Extension_Demo',

    packages = find_packages(),

    ext_package = 'custom_lib',

    ext_modules = [Extension('custom_module',['custom_lib/custom_module.c'])],

    entry_points = {'console_scripts': ['custom-lib-cli = custom_lib.custom_module:custom_hello', ], },

)

Install the custom_lib by running the below command in directory where your setup.py exists

❯ pip install .

Output

The output of the above command should be something like this,

❯ Successfully built custom-lib

❯ Successfully installed custom-lib-0.1

Now check if the custom_lib works, with the cli command given in entry_points

❯ custom-lib-cli

Output

The output of the above command depends on your entry_points!

here,

❯ Hello from Custom Lib

One final step to integrate the extension module with the application.

Recipe

https://python-for-android.readthedocs.io/en/latest/recipes/

Recipes are special scripts for compiling and installing different programs (including Python modules) into a p4a distribution. They are necessary to take care of compilation for any compiled components, as these must be compiled for Android with the correct architecture.

Directory Structure for Recipe

 python-for-android
 |
 └── recipe
       |
       └── custom_lib
               |
               └── __init__.py

__init__.py

from pythonforandroid.recipe import CompiledComponentsPythonRecipe

class BillBookLibRecipe(CompiledComponentsPythonRecipe):

        site_packages_name = 'custom_lib'
        depends = ['setuptools']
        call_hostpython_via_targetpython = False


        def should_build(self, arch):
                return True

recipe = BillBookLibRecipe()

Buildozer

buildozer.spec

# In requirements make sure to mention the C Extension Module
requirements = python3,kivy,custom_lib

# Specify the path for the setup.py / setup.cfg for local C Extension Module
requirements.source.custom_lib = ./custom_lib/

# Specify the path for Recipe for local C Extension Module
p4a.local_recipes = ./python-for-android/recipe