# Python Kivy Framework

Kivy is an open source Python library for rapid development of applications that make use of innovative user interfaces, such as multi-touch apps. It runs on Linux, Windows, OS X, Android, iOS, and Raspberry Pi.

## Installation

```bash
pip install kivy
```

## Basic Application

To create a Kivy app, you subclass the `App` class and implement the `build()` method, returning a widget tree.

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

class MyApp(App):
    def build(self):
        return Label(text='Hello world')

if __name__ == '__main__':
    MyApp().run()
```

## Layouts

Kivy uses layouts to arrange widgets. `BoxLayout` is one of the most common.

```python
from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.boxlayout import BoxLayout

class MenuApp(App):
    def build(self):
        layout = BoxLayout(orientation='vertical')
        
        btn1 = Button(text='Start Game')
        btn2 = Button(text='Settings')
        btn3 = Button(text='Exit')
        
        layout.add_widget(btn1)
        layout.add_widget(btn2)
        layout.add_widget(btn3)
        
        return layout

if __name__ == '__main__':
    MenuApp().run()
```

## Handling Events

You can bind callbacks to events like `on_press`.

```python
def on_button_press(instance):
    print(f'You pressed {instance.text}')

btn = Button(text='Click Me')
btn.bind(on_press=on_button_press)
```

## The KV Language

Kivy allows you to separate logic (Python) from presentation (KV Language).

**myapp.py**:
```python
class LoginScreen(GridLayout):
    pass
```

**myapp.kv**:
```yaml
<LoginScreen>:
    cols: 2
    Label:
        text: 'User Name'
    TextInput:
        multiline: False
```

[[programming/python/python]]