How to build mobile apps with Python

#Introduction

When we talk python, we don’t normally include building mobile apps, this is because these python frameworks are not fully optimized to build a production ready applications.

Nevertheless, we are going to checkout kivy in this tutorial to build and deploy a simple mobile app.

#Prerequsite

• Have a little understanding of OOP(Object Oriented Programming)
• Apps are not production ready

#Installing

To use kivy we need to get it on our machine

run

$ pip install kivy

#Create a simple hello world app

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

class MainApp(App):
    def build(self):
        return Label(text='Hello World')

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

• The imports are straight forward and clear
• In our class, it inherits from the App class we imported.
• In the build function we return the object that would takeup our window

in our case an Hello World label

#Taking it further

We definitly don’t want just a label or button on our app, this is where layouts comes in and we are going to build an app that takes a person name as an input and Greets Them when they press the Greet button.

#Layouts, Inputs and Buttons

There are fundamentally two types of layout

• Vertical
• Horizontal

Grids and others are derived from those.

We are going to use kivy’s BoxLayout to create a vertical and horizontal layout

from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.textinput import TextInput

class Great(BoxLayout):
    def __init__(self):
        super().__init__()
        self.orientation = 'vertical'

        self.greet_label = Label(text='Greet')
        self.user_name = TextInput()
        self.greet_button = Button(text='Greet')

        # adds the widgets to our BoxLayout
        self.add_widget(self.greet_label)
        self.add_widget(self.user_name)
        self.add_widget(self.greet_button)

class MainApp(App):
    def build(self):
        return Great()

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

#Taking the code apart

• The imports are straight forward and clear
• We now have a new class which inherit from BoxLayout
  we used super to call the init from the inherited function.
  we set the orientation to vertical cause by BoxLayout is horizontal by defualt.
• created new components and added them to our BoxLayout
• the build function now returns the Greet class

#The Functions

What left for our app is to greet the user whenever it enters it name and press the greet button.

from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.textinput import TextInput


class Great(BoxLayout):
    def __init__(self):
        super().__init__()
        self.orientation = 'vertical'
        self.greet_label = Label(text='Greet')
        # setting a custom font size for the greet label

        self.greet_label.font_size = 40
        self.user_name = TextInput()
        self.greet_button = Button(text='Greet')
        self.greet_button.on_press = self.great_user
        self.add_widget(self.greet_label)
        self.add_widget(self.user_name)
        self.add_widget(self.greet_button)

    def great_user(self):
        """This function get the name from the textinput
        and set the text of the greet_label to a message for the user
        """
        # get the text from self.user_name
        user_name = self.user_name.text

        # set the text for the label
        self.greet_label.text = f"Hello {user_name}"

        # clear the self.user_name text input

        self.user_name.text = ''


class MainApp(App):
    def build(self):
        return Great()


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

Compile

kivy apps are compiled using buildozer

See buildozer documentation