Kivy label code from kivy language to python

Question

I have the following simple application created with kivy gui framework. It is not the simplest one since label_1 has background color and its size is modified according to the text of the label. This is my very first experience with kivy. Unfortunately, kivy documentation and most of the examples accessible via google heavily use kivy language. My qestion is: how can I get the same result without kivy language using only python 3?

Code:

from kivy.config import Config
from kivy.core.window import Window

from kivy.app import App

from kivy.lang import Builder


MainScreen = Builder.load_string('''
BoxLayout:
    orientation: 'vertical'
    Label:
        text: 'label_1'
        font_size: 18
        color: (0, 0, 0, 1)
        size_hint: None, None
        size: self.texture_size
        canvas.before:
            Color:
                rgba: 1, .5, 0, 1
            Rectangle:
                pos: self.pos
                size: self.size
    Label:
        text: 'label_2'
        color: (0, 0, 0, 1)
''')


class MyApp(App):
    def build(self):
        return MainScreen


if __name__ == '__main__':

    Config.set('input', 'mouse', 'mouse,multitouch_on_demand')
    Window.clearcolor = (1, 1, 1, 1)

    MyApp().run()

How it looks:

Answer 1

The implementation of the code that you require is:

from kivy.config import Config
from kivy.core.window import Window
from kivy.app import App

from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.graphics import Rectangle, Color

mainscreen = BoxLayout(orientation='vertical')

label1 = Label(text='label_1', font_size=18, color=(0, 0, 0, 1), size_hint=(None, None))
label1.bind(texture_size=label1.setter('size'))
def update_rect(instance, *args):
    rect.pos = instance.pos
    rect.size = instance.size
with label1.canvas.before:
    Color(1, .5, 0, 1)
    rect = Rectangle(pos=label1.pos, size=label1.size)
label1.bind(pos=update_rect, size=update_rect)

label2 = Label(text='label_2', color=(0, 0, 0, 1))

mainscreen.add_widget(label1)
mainscreen.add_widget(label2)

class MyApp(App):
    def build(self):
        return mainscreen

if __name__ == '__main__':
    Config.set('input', 'mouse', 'mouse,multitouch_on_demand')
    Window.clearcolor = (1, 1, 1, 1)
    MyApp().run()

IMHO the implementation in kv is more readable and more flexible when done binding as in the case of the label that fits the size.

---

from kivy.config import Config
from kivy.core.window import Window
from kivy.app import App

from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.graphics import Rectangle, Color

from kivy.properties import ListProperty


class CustomLabel(Label):
    bgcolor = ListProperty([0, 0, 0, 1])
    def __init__(self, **kwargs):
        if kwargs.get('bgcolor'):
            self.bgcolor = kwargs['bgcolor']
            kwargs.pop('bgcolor')
        super(CustomLabel, self).__init__(**kwargs)
        self.bind(texture_size=self.setter('size'))

        with self.canvas.before:
            self.p = Color(*self.bgcolor)
            self.rect = Rectangle(pos=self.pos, size=self.size)

        self.on_bgcolor()
        self.bind(pos=self.geometry_bind, size=self.geometry_bind)

    def on_bgcolor(self, *args):
        self.p.rgba = self.bgcolor

    def geometry_bind(self, *args):
        self.rect.pos = self.pos
        self.rect.size = self.size


class MyApp(App):
    def build(self):
        mainscreen = BoxLayout(orientation='vertical')
        label1 = CustomLabel(text='label_1', font_size=18, color=(0, 0, 0, 1), size_hint=(None, None), bgcolor=(1, .5, 0, 1))
        label2 = Label(text='label_2', color=(0, 0, 0, 1))
        mainscreen.add_widget(label1)
        mainscreen.add_widget(label2)
        return mainscreen

if __name__ == '__main__':
    Config.set('input', 'mouse', 'mouse,multitouch_on_demand')
    Window.clearcolor = (1, 1, 1, 1)
    MyApp().run()

Explanation:

• bind: the bind(foo_property = callback) function is responsible for calling the callback when foo_property changes.

• setter: the setter('foo_property') function generates a callback that allows you to set a value.

If you join both functions:

class FooClass(Foo_EventDispatcher):
    property_a = FooProperty(initial_value_a)
    property_b = FooProperty(initial_value_b)

    def __init__(self, **kwargs):
       super(FooClass, self).__init__(**kwargs)
       self.bind(property_a=self.setter('property_b'))

equivalent to the following instruction in .kv:

<FooClass>:
    property_b: self.property_a