Pass variables from .py to .kv file

Question

I am trying to use variables from python file to .kv file so I searched similar questions and found out the way use Property and coded like this:

Answer 1

There are two solutions to this problem. Please refer to the solutions and example for details.

Solution 1: kv file - Using If statement

The variable, abcd is None when the kv file is parsed. Add if...else... statement to solve the problem.

Snippet - kv file

<MyButton@Button>:
    text: "" if app.abcd is None else "contents (%s)"%(app.abcd)

    background_color: (255, 255, 255,1)    # white background color
    color: 0, 0, 0, 1    # black color text

Solution 2: Python code - Initialize in build() method

Initialize variable, abcd in the build() method.

Snippet - Python code

class TestApp(App):
    abcd = StringProperty('')

    def build(self):
        self.abcd = 'test'
        return ScreenManagement()

Example

main.py

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import StringProperty


class StationTest(Screen):
    pass


class ScreenManagement(ScreenManager):
    pass


class TestApp(App):
    abcd = StringProperty('test')

    def build(self):
        return ScreenManagement()


TestApp().run()

test.kv

#:kivy 1.11.0
#:import SlideTransition kivy.uix.screenmanager.SlideTransition

<ScreenManagement>:
    transition: SlideTransition(direction='left')
    StationTest:

<StationTest>:
    name: 'StationTest'
    BoxLayout:
        orientation: 'vertical'
        size_hint: 1, 0.35
        padding: 0, -200, 0, 0
        MyButton:
        MyButton:
        MyButton:
        MyButton:



<MyButton@Button>:
    # text: "" if app.abcd is None else "contents (%s)"%(app.abcd)
    text: "contents (%s)"%(app.abcd)

    background_color: (1, 1, 1, 1)    # white background
    color: 0, 0, 0, 1    # black color text

Output