Standalone Android Apps in Python

Baptiste Lagarde

Sydney Python Group, 2013.11.07

I. Toolchain
II. Kivy

java app vs. python app

Python cross-compiled for ARM using the Android NDK

Android NDK - The Native Development Kit allows you to implement parts of your app using native-code languages such as C and C++.

I. Toolchain

toolchain (1/5)

Overview

http://python-for-android.readthedocs.org/en/latest/toolchain/

Toolchain (2/5)

Prerequisites ~6GB (sigh)

Option B

Option A

Download Android SDK + NDK
Follow pages and pages of Google instructions
Download more stuff from inside Eclipse (?!)
Set-up some environment variables
git clone ..., pip install ...

Download .vbi virtual machine image
Run with virtualbox

Toolchain (2/5)

Toolchain (2/5)

Toolchain (3/5)

Distribute

Cross-compilation

kivy@kivy-VirtualBox:~/android/python-for-android$ ./distribute.sh -m kivy

Creates a host Python
Compiles an ARM Python
Opt-in recipes with -m

Modules

Some Standard Library modules excluded by default to save space

Pure python modules can simply be included with the app's code

Many modules are available as "recipes"

Toolchain (4/5)

Make Kivy App

Kivy - Open source Python library for rapid development of applications that make use of innovative user interfaces, such as multi-touch apps.

# test.py
import kivy

from kivy.app import App
from kivy.uix.button import Button

class TestApp(App):
    def build(self):
        return Button(text='Hello World')

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

$ python test.py

TOOLCHAIN (5/5)

Build and Install

Build

$ cd ~/android/python-for-android/dist/default$ ./build.py --package com.example.myapp --name "MyApp" --version 1 --dir /path/to/kivy/app/ debug

Install

Phone: Settings > Developer options > USB debugging

$ adb install bin/MyApp-1-debug.apk

...or simply open the .apk on the phone (transfer by email, USB, Dropbox, ...)

Toolchain (5/5)

II. Kivy

The KV language
Accessing the hardware
Useful resources

Kivy (1/5)

Example app

(Saves the phone's accelerometer readings to CSV)

Kivy (2/5)

The KV Language

Features

Move UI declaration to separate file

Root widget
Templates
Widget classes, inheritance

Anything right of ":" is Python!
Python imports
Event bindings , e.g. on_press
Keyword arguments
Hooks, e.g. id, root, app, self

BoxLayout:
    orientation: "vertical"
    Label:
        id: intro
    TextInput:
        id: path
        multiline: False
        on_text_validate: app.setpath()
    Label:
        id: progress
    BoxLayout:
        orientation: "horizontal"        Button:
            text: "Start capture"
            on_press: app.start()
        Button:
            text: "Stop capture"
            on_press: app.stop()
        Button:
            text: "Quit"
            on_press: exit()

Kivy (3/5)

Accessing the hardware with pyjnius

pyjnius - Python module to access Java classes as Python classes, using JNI.

JNI - The Java Native Interface is a programming framework that enables Java code running in a Java Virtual Machine to call, and to be called by, native applications and libraries written in other languages

(iOS -> See pyobjus)

 >>> from jnius import autoclass
 >>> Hardware = autoclass('org.renpy.android.Hardware')
 >>> Hardware.accelerometerEnable(True)
 >>> print Hardware.accelerometerReading()
 [0.11400000005960464, -0.19099999964237213, 9.5380001068115234]

Kivy (4/5)

Kivy remote shell

Useful to try out or troubleshoot hardware-related functions

Install Remote Kivy App
SSH to a Python prompt
Poke around

$ ssh -p8000 admin@192.168.1.3
admin@192.168.1.3's password: # "kivy">>> import platform
>>> platform.machine()
'armv7l'
>>> from jnius import autoclass
>>> TextToSpeech = autoclass('android.speech.tts.TextToSpeech')
>>> PythonActivity = autoclass('org.renpy.android.PythonActivity')
>>> tts = TextToSpeech(PythonActivity.mActivity, None)
>>> tts.speak('Hello World.', TextToSpeech.QUEUE_FLUSH, None)
>>> tts.speak('999999999999', TextToSpeech.QUEUE_FLUSH, None)  # haha